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Journal articles on the topic 'Spiral bulges'

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Author: Grafiati

Published: 11 March 2023

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1

Thomas, Daniel, and Roger L. Davies. "Rejuvenation of spiral bulges." Proceedings of the International Astronomical Union 3, S245 (July 2007): 289–92. http://dx.doi.org/10.1017/s1743921308017936.

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AbstractWe seek to understand whether the stellar populations of galactic bulges show evidence of secular evolution triggered by the presence of the disc. To this end we re-analyse the sample of Proctor & Sansom (2002), deriving stellar population ages and element abundances from absorption line indices as functions of central velocity dispersion and Hubble type. In agreement with other studies in the literature, we find that bulges have relatively low luminosity weighted ages, the lowest age derived being 1.3 Gyr. Hence bulges are not generally old, but actually rejuvenated systems. We discuss evidence that this might be true also for the bulge of the Milky Way. The smallest bulges are the youngest with the lowest α/Fe ratios indicating the presence of significant star formation events involving 10 − 30 per cent of their total mass in the past 1 − 2 Gyr. No significant correlations of the stellar population parameters with Hubble Type are found. We show that the above relationships with σ coincide perfectly with those of early-type galaxies. At a given velocity dispersion, bulges and elliptical galaxies are indistinguishable as far as their stellar populations are concerned. These results favour an inside-out formation scenario and indicate that the discs in spiral galaxies of Hubble types Sbc and earlier cannot have a significant influence on the evolution of the stellar populations in the bulge component. The phenomenon of pseudobulge formation must be restricted to spirals of types later than Sbc.

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2

Kumar, Ankit, Mousumi Das, and Sandeep Kumar Kataria. "Galaxy flybys: evolution of the bulge, disc, and spiral arms." Monthly Notices of the Royal Astronomical Society 506, no. 1 (June 22, 2021): 98–114. http://dx.doi.org/10.1093/mnras/stab1742.

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ABSTRACT Galaxy flybys are as common as mergers in low-redshift Universe and are important for galaxy evolution as they involve the exchange of significant amounts of mass and energy. In this study, we investigate the effect of minor flybys on the bulges, discs, and spiral arms of Milky Way mass galaxies for two types of bulges – classical bulges and boxy/peanut pseudo-bulges. Our N-body simulations comprise of two disc galaxies of mass ratios 10:1 and 5:1, where the discs of the galaxies lie in their orbital plane and the pericentre distance is varied. We performed photometric and kinematic bulge–disc decomposition at regular time-steps and traced the evolution of the disc size, spiral structure, bulge sersic index, bulge mass, and bulge angular momentum. Our results show that the main effect on the discs is disc thickening, which is seen as the increase in the ratio of disc scale height to scale radius. The strength of the spiral structure A2/A0 shows small oscillations about the mean time-varying amplitude in the pseudo-bulge host galaxies. The flyby has no significant effect on non-rotating classical bulge, which shows that these bulges are extremely stable in galaxy interactions. However, the pseudo-bulges become dynamically hotter in flybys indicating that flybys may play an important role in accelerating the rate of secular evolution in disc galaxies. This effect on pseudo-bulges is a result of their rotating nature as part of the bar. Also, flybys do not affect the time and strength of bar buckling.

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3

Kim, Eunbin, Sungsoo S. Kim, Yun-Young Choi, Gwang-Ho Lee, Richard de Grijs, Myung Gyoon Lee, and Ho Seong Hwang. "Nuclear starburst activity induced by elongated bulges in spiral galaxies." Monthly Notices of the Royal Astronomical Society 479, no. 1 (June 5, 2018): 562–69. http://dx.doi.org/10.1093/mnras/sty1451.

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ABSTRACT We study the effects of bulge elongation on the star formation activity in the centres of spiral galaxies using the data from the Sloan Digital Sky Survey Data Release 7. We construct a volume-limited sample of face-on spiral galaxies with Mr < −19.5 mag at 0.02 ≤ $z$ < 0.055 by excluding barred galaxies, where the aperture of the SDSS spectroscopic fibre covers the bulges of the galaxies. We adopt the ellipticity of bulges measured by Simard et al., who performed two-dimensional bulge + disc decompositions using the SDSS images of galaxies, and identify nuclear starbursts using the fibre specific star formation rates derived from the SDSS spectra. We find a statistically significant correlation between bulge elongation and nuclear starbursts in the sense that the fraction of nuclear starbursts increases with bulge elongation. This correlation is more prominent for fainter and redder galaxies, which exhibit higher ratios of elongated bulges. We find no significant environmental dependence of the correlation between bulge elongation and nuclear starbursts. These results suggest that non-axisymmetric bulges can efficiently feed the gas into the centre of galaxies to trigger nuclear starburst activity.

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4

Richer, Michael G., and Marshall L. McCall. "Several evolutionary channels for bright planetary nebulae." Proceedings of the International Astronomical Union 11, S317 (August 2015): 344–45. http://dx.doi.org/10.1017/s1743921315008832.

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AbstractThe populations of bright planetary nebulae in the discs of spirals appear to differ in their spectral properties from those in ellipticals and the bulges of spirals. The bright planetary nebulae from the bulge of the Milky Way are entirely compatible with those observed in the discs of spiral galaxies. The similarity might be explained if the bulge of the Milky Way evolved secularly from the disc, in which case the bulge should be regarded as a pseudo-bulge.

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5

MacArthur, Lauren A., Richard S. Ellis, and Tommaso Treu. "The fundamental plane of bulges at intermediate redshift." Proceedings of the International Astronomical Union 3, S245 (July 2007): 443–46. http://dx.doi.org/10.1017/s1743921308018322.

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AbstractWe report on a new study aimed at understanding the diversity and evolutionary properties of distant galactic bulges in the context of well-established trends for pure spheroidal galaxies. Bulges have been isolated for a sample of 137 spiral galaxies in the GOODS fields within the redshift range 0.1 < z < 1.2. Using proven photometric techniques we determine for each galaxy the characteristic parameters (size, surface brightness, profile shape) in the 4 GOODS-ACS imaging bands of both the disk and bulge components. Using the DEIMOS spectrograph on Keck, precision stellar velocity dispersions were secured for a sizeable fraction of the bulges. This has enabled us to compare the Fundamental Plane of our distant bulges with that of field spheroidal galaxies in a similar redshift range. Bulges in spiral galaxies with a bulge-to-total luminosity ratio (B/T) > 0.2 show very similar patterns of evolution to those seen for low luminosity spheroidals. To first order, their recent mass assembly histories are equivalent.

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6

Bureau, M., and K. C. Freeman. "The Nature of Boxy/Peanut Spiral Galaxies: Overview and New Results." Publications of the Astronomical Society of Australia 14, no. 2 (1997): 146–58. http://dx.doi.org/10.1071/as97146.

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AbstractThe formation mechanism of boxy/peanut-shaped bulges in spiral galaxies has been a problem for many years. We briefly review here the possible formation scenarios for boxy/peanut bulges, concentrating on both the bar-buckling and accretion hypotheses, and then describe an observational program aimed at testing those various theories and studying the vertical structure of edge-on bars. Our program includes optical long-slit spectroscopy, Hiline-imaging, near-infrared imaging, and multi-band optical imaging. New spectroscopic results (both optical and Hi) are presented on seven galaxies, including five boxy/peanut-bulge spirals. Based on Kuijken & Merrifield's (1995) idea for detecting edge-on bars, we argue that these observations constitute a strong case in favour of the bar-buckling mechanism for the formation of boxy/peanut-shaped bulges, but they also raise many questions and prompt for more detailed modelling to be made. The implications of the observations concerning the determination of rotation curves and of the physical conditions in bulges are also discussed.

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7

Mengistu, Petra, and Karen L. Masters. "Mass and Color Dependence of the Hubble Spiral Sequence." Research Notes of the AAS 7, no. 3 (March 3, 2023): 35. http://dx.doi.org/10.3847/2515-5172/acc032.

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Abstract In the classic Hubble spiral sequence, arm windiness correlates with bulge size; Sa type spiral galaxies with larger bulges also have the most tightly wound spirals. Exceptions to this have long been known, and in recent work using Galaxy Zoo morphologies no strong correlation was seen in a volume limited sample. In this Research Note, we explore the impact of galaxy mass and integrated color upon this correlation in the Galaxy Zoo sample, finding that bluer and lower mass spirals show the “expected” correlation; however, it becomes slightly negative for redder and/or more massive spiral galaxies.

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8

Laurikainen, E., H. Salo, R. Buta, and J. H. Knapen. "Overview of the Near-IR S0 Galaxy Survey (NIRS0S)." Advances in Astronomy 2011 (2011): 1–17. http://dx.doi.org/10.1155/2011/516739.

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An overview of the results of the near-IR S0 galaxy survey (NIRS0S) is presented. NIRS0S is a magnitude- (mB⩽12.5 mag) and inclination- (<65∘) limited sample of ̃200 nearby galaxies, mainly S0s, but includes also Sa and E galaxies. It uses deepKs-band images, typically reaching a surface brightness of 23.5 mag arcsec−2. Detailed visual and photometric classifications were made, for the first time coding also the lenses in a systematic manner. As a comparison sample, a similar sized spiral galaxy sample with similar image quality was used. Based on our analysis, the Hubble sequence was revisited: following the early idea by van den Bergh we suggested that the S0s are spread throughout the Hubble sequence in parallel tuning forks as spirals (S0a, S0b, S0c, etc.). This is evidenced by our improved bulge-to-total (B/T) flux ratios in the S0s, reaching small values typical to late-type spirals. The properties of bulges and disks in S0s were found to be similar to those in spirals and, also, the masses and scale parameters of the bulges and disks to be coupled. It was estimated that the spiral bulges brighter than −20 mag inK-band are massive enough to be converted into the bulges of S0s merely by star formation. Bars were found to be fairly robust both in S0s and spirals, but, inspite of that, bars might evolve significantly within the Hubble sequence.

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9

MacArthur, Lauren A., J. Jesús González, Stéphane Courteau, and Michael McDonald. "Stellar Populations and Kinematics in Spiral Galaxies." Proceedings of the International Astronomical Union 5, S262 (August 2009): 172–75. http://dx.doi.org/10.1017/s1743921310002735.

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AbstractWe present a detailed study of the stellar populations (SPs) and kinematics of the bulge and inner disk regions of nearby spiral galaxies (Sa-Sd) based on deep long-slit Gemini/GMOS data. We find that the SPs of spiral galaxies are not well matched by single episodes of star formation; representative SPs must involve average SP values integrated over the star formation history (SFH) of the galaxy, such as those derived from the “full population synthesis” method used here. Our spiral bulges follow the same correlations of increasing light-weighted age and metallicity with central velocity dispersion as those of elliptical galaxies and early-type bulges found in other studies, but when SFHs more complex and realistic than a single burst are invoked, the trend with age is shallower and its scatter much reduced. In a mass-weighted context, all bulges are predominantly composed of old and metal-rich SPs. Bulge formation appears to be dominated by early processes that are common to all spheroids, whether they currently reside in disks or not. While monolithic collapse cannot be ruled out in some cases, merging must be invoked to explain the SP gradients in most bulges. Further bulge growth via secular processes, or “rejuvenated” star formation, generally contributes minimally to the stellar mass budget. We also demonstrate how the combination of our full population synthesis modeling of high-quality optical spectra of integrated SPs along with optical-NIR broad-band imaging can single out potential model weaknesses and help determine the reliability of the inferred SFHs.

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10

Pastrav, Bogdan A. "On the scaling relations of bulges and early-type galaxies." Monthly Notices of the Royal Astronomical Society 506, no. 1 (June 21, 2021): 452–67. http://dx.doi.org/10.1093/mnras/stab1746.

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ABSTRACT Following from our recent work, we present here a detailed structural analysis of a representative sample of nearby spiral and early-type galaxies (ETGs) taken from the Key Insights on Nearby Galaxies: a Far-Infrared Survey with Herschel/ (KINGFISH) / Spitzer Infrared Nearby Galaxies Survey (SINGS) surveys. The photometric parameters of bulges are obtained from bulge-disc decompositions using Galfi data analysis algorithm. The method and corrections for projection and dust effects previously obtained are used to derive intrinsic photometric and structural bulge parameters. We show the main bulge scaling relations and the black hole relations, both observed and intrinsic ones, in B band. We find dust and inclination effects to produce more important changes in the parameters of the Kormendy relation for spiral galaxies, with the respective bulges of late-type galaxies (LTGs) residing on a steeper slope relation than the early-type galaxies (ETGs). We observe that the Kormendy relation in combination with a bulge Sérsic index (nb) threshold does not produce a conclusive morphological separation of bulges. The nb- bulge-to-total flux ratio (B/T) and B/T-stellar mass could be used to discriminate between LTGs and ETGs, while a further use of these parameters to divide bulges with different morphologies is problematic due to overlaps in the two distributions or large spread in values. We confirm the existence of two distinct intrinsic relations between the bulge luminosity (or absolute magnitude) and Sérsic index for LTGs and ETGs, while the relations between the black hole mass (MBH) and bulge luminosity are not found to be statistically different at p<0.05. Within errors, we find statistically similar intrinsic MBH − nb relations for all bulges.

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11

Khochfar, Sadegh. "The hierarchical build-up of bulges in CDM." Proceedings of the International Astronomical Union 3, S245 (July 2007): 55–58. http://dx.doi.org/10.1017/s1743921308017274.

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AbstractWe investigate the hierarchical build-up of stars in bulges within the standard Λ-cold dark matter scenario. By separating the population into stars born during starbursts that accompany the formation of spheroids in major mergers (starburst component), and stars that are previously formed in discs of progenitor galaxies (quiescent component) and added to the spheroid by dynamical interaction. Our results are summarised as follows: bulges that form early have larger starburst fraction and hence should be smaller than their counter parts that form later. The quiescent fraction in bulges is an increasing function of bulge mass, becoming constant at Mq/Mbul ~ 0.8, mainly due to the infall of satellite galaxies that contribute disc stars to the bulge. Minor mergers are an order of magnitude more frequent than major mergers and must play a significant role in the evolution of bulges. Above the critical mass Mc ~ 3 × 1010 M⊙ most of the stars in the universe are in spheroids, which at high redshift are exclusively elliptical galaxies and at low redshifts partly bulges. Due to the enhanced evolution of galaxies ending up in high density environments, the starburst fraction and the surface mass densities of bulges below Mc should be enhanced with respect to field galaxies. Dissipation during the formation of massive bulges in present day early-type spirals is less important than for the formation of present day elliptical galaxies of the same mass thereby explaining the possible difference in phase-space densities between spiral galaxies and elliptical galaxies.

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12

Bureau, M., and K. C. Freeman. "Formation of Boxy/Peanut-Shaped Bulges in Spiral Galaxies: Accretion or Bar Instability?" Symposium - International Astronomical Union 186 (1999): 193. http://dx.doi.org/10.1017/s0074180900112537.

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Boxy/peanut-shaped bulge galaxies constitute at least 20-30% of all spirals. Distribution functions and numerical simulations studies have shown that the slow decay of the orbit of a companion into a larger spiral can lead to the formation of a boxy/peanut bulge. However, the bar-buckling instability now appears a more likely process. Thin bars either do not form or, as shown by N-body simulations, buckle and settle with an increased thickness, appearing boxy or peanut-shaped when seen edge-on. This project aims to determine the dynamical state of a sample of 30 edge-on spirals, 3/4 of which have boxy/peanut-shaped bulges, half having close-by companions.

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13

Thomas, D., and R. L. Davies. "Rejuvenation of spiral bulges." Monthly Notices of the Royal Astronomical Society 366, no. 2 (February 21, 2006): 510–20. http://dx.doi.org/10.1111/j.1365-2966.2005.09871.x.

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14

Sansom, A. E., S. I. Loubser, P. Sánchez-Blázquez, and I. K. Söchting. "Observations across nearby spiral bulges." Proceedings of the International Astronomical Union 3, S245 (July 2007): 141–42. http://dx.doi.org/10.1017/s1743921308017511.

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AbstractThe bulges of spiral galaxies may be old, as in our Galaxy, or may possess younger stars, as evidenced in spectroscopic line strengths in some external bulges. Bulges look similar to elliptical galaxies, but their formation history is expected to differ due to the presence of the disc and different formation mechanisms. This project extends the numbers of high signal-to-noise, broad coverage spectra to a larger sample of bulges in order to test conflicting ideas about their age distributions. New Gemini long-slit observations will be used to derive stellar population ages and histories across 30 bulges. Here we present preliminary results from the sample.

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15

Zhang, Xiaolei. "1.7. Secular dynamical evolution of spiral galaxies and the formation of galactic bulges." Symposium - International Astronomical Union 184 (1998): 29–30. http://dx.doi.org/10.1017/s0074180900083868.

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We show that a recently discovered spiral-induced radial mass accretion process could account for the formation of the Galactic Bulge in a Hubble time. This process is thus expected to be important in the formation of bulges in spiral galaxies, and in the secular evolution of galaxies along the Hubble sequence from late to earlier types.

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16

Itoh, Nobunari, and Takashi Ichikawa. "1.20. The color-magnitude relation of bulges." Symposium - International Astronomical Union 184 (1998): 55–56. http://dx.doi.org/10.1017/s0074180900083996.

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One of the main aims with respect to the evolution of spiral galaxies is to clarify how the disk and bulge were formed. The study of bulges has usually been focused on how bulges resemble to elliptical galaxies. For the study of the evolution of elliptical galaxies, the color-magnitude relation (C-M relation) gives us a clue to understanding the formation and evolution of ellipticals. In fact, the tight C-M relation of ellipticals (Bower et al. 1992) was interpreted as the sequence of the metallicity difference (Kodama and Arimoto 1997). On the contrary, there are few observations for the C-M relation of bulges. On the analogy of elliptical galaxies, the C-M relation of bulges, if it exists, may be one of the most important clues to understanding the formation process of bulges. The main goal of the present study is to investigate the C-M relation of bulges.

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17

Ballero, Silvia K., Francesca Matteucci, and Luca Ciotti. "Chemical evolution of Seyfert galaxies." Proceedings of the International Astronomical Union 3, S245 (July 2007): 231–32. http://dx.doi.org/10.1017/s1743921308017729.

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AbstractWe computed the chemical evolution of Seyfert galaxies, residing in spiral bulges, based on an updated model for the Milky Way bulge with updated calculations of the Galactic potential and of the feedback from the central supermassive black hole (BH) in a spherical approximation. We followed the evolution of bulges of masses 2 × 109 − 1011M⊙ by scaling the star-formation efficiency and the bulge scalelenght as in the inverse-wind scenario for ellipticals. We successfully reproduced the observed relation between the BH mass and that of the host bulge, and the observed peak nuclear bolometric luminosity. The observed metal overabundances are easily achieved, as well as the constancy of chemical abundances with the redshift.

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18

Varela, A. M., E. Simonneau, and C. Muñoz–Tuñón. "Triaxiality in the bulges of spirals: dynamical implications." Symposium - International Astronomical Union 153 (1993): 435–36. http://dx.doi.org/10.1017/s0074180900123952.

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The presence of triaxial bulges has been suggested as a mechanism for sweeping out the interstellar gas into the nuclear zones of normal spiral galaxies, giving rise to star formation processes (Zaritsky and Lo, 1986). In an initial phase of the present study, we have analysed the bulge component of a sample of spiral galaxies, obtained using the 4.2m WHT at La Palma Observatory, selected from among those which exhibit moderate activity. The results obtained are: (a) There is evidence, from the misalignment between the semi–major axes of the isophotes of the bulge and disc components, to support the presence of triaxial bulges in these galaxies; (b) The high spatial resolution of the images allows us to sample the bulges, showing that the surface brightness distribution is not always represented by a family of homologous coaxial ellipses, but rather by a set of ellipses which precess around a common centre, and whose ellipticity varies (see Beckman et al., 1991; Varela, 1992). It is possible to reproduce this structure with a family of concentric triaxial ellipsoidal shells. The presence of a disc offers the advantage of enabling us to interpret the geometry of the bulge correctly, but poses the disadvantage of requiring to interpret the disc emission in order to reconstruct that associated only with the bulge, i.e. to decontaminate the bulge from the disc light. To this end we carried out a photometric analysis, which enabled us to effect a valid bulge/disc decomposition. The preliminary results yielded by the analysis of the bulge component (after decontaminating the disc) show the presence of “transparent” discs in the galaxies analysed.

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19

Byun, Yong-Ik. "1.13. Structural characteristics of spiral bulges." Symposium - International Astronomical Union 184 (1998): 41–42. http://dx.doi.org/10.1017/s0074180900083923.

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Recently it has been suggested that some bulges are really disks (Kormendy 1993). He argues that some bulges are not spheroidal components of steep luminosity distribution like elliptical galaxies but actually parts of flat disks, whose central luminosity profiles are steeper than the inward extrapolation of an exponential fit to the outer parts. The existence of disk-like bulges strongly supports the idea of disk secular evolution.

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20

Dettmar, R. J., and A. Ferrara. "NIR Imaging of the Box/Peanut Bulge in NGC 4302." Symposium - International Astronomical Union 171 (1996): 362. http://dx.doi.org/10.1017/s0074180900232816.

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The central, spheroidal component of spiral galaxies is frequently found to be “box- or peanut” (b/p) shaped. More than 30% of edge-on galaxies may show this phenomenon (Dettmar 1995). To explain this large frequency a very common process for the origin of this specific shape is required. N-body simulations have shown that this can be attributed to instabilities and resonances caused by bars in spiral disks (e. g., Combes et al. 1990, Raha et al. 1991).Previous statistics (Jarvis 1986, Shaw 1987, de Souza & dos Anjos 1987) are hampered by the low dynamic range of the photographic material used as well as by dust absorption in late type spirals and the difficulty to disentangle disk and bulge in such systems. We present K-band imaging of the very dusty edge-on galaxy NGC 4302 in the Virgo cluster supporting the presence of b/p bulges in late type spirals.NIR Observations were obtained with the NICMOS-3 ARNICA camera at TIRGO1 in spring 1994. The combined image of NGC 4302 clearly shows a flat-top “boxy” structure of the spheroid and an additional very thin component appears on the major axis cut. This latter component could be identified with a bar. The example of NGC 4302 demonstrates that b/p bulges are indeed present in disks of late type spirals and that bars can account for a significant fraction of these structures. As a consequence, the bulge/disk ratio of late type spirals has to be interpreted in an evolutionary scenario rather than as a primordial property.

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21

Erwin, Peter, Roberto Saglia, Jens Thomas, Maximilian Fabricius, Ralf Bender, Stephanie Rusli, Nina Nowak, John E. Beckman, and Juan Carlos Vega Beltrán. "Using 3D Spectroscopy to Probe the Orbital Structure of Composite Bulges." Proceedings of the International Astronomical Union 10, S309 (July 2014): 359–60. http://dx.doi.org/10.1017/s1743921314010503.

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AbstractDetailed imaging and spectroscopic analysis of the centers of nearby S0 and spiral galaxies shows the existence of “composite bulges”, where both classical bulges and disky pseudobulges coexist in the same galaxy. As part of a search for supermassive black holes in nearby galaxy nuclei, we obtained VLT-SINFONI observations in adaptive-optics mode of several of these galaxies. Schwarzschild dynamical modeling enables us to disentangle the stellar orbital structure of the different central components, and to distinguish the differing contributions of kinematically hot (classical bulge) and kinematically cool (pseudobulge) components in the same galaxy.

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Driver, Simon P., Jochen Liske, and Alister W. Graham. "The Millennium Galaxy Catalogue: Galaxy Bimodality." Proceedings of the International Astronomical Union 2, S235 (August 2006): 17–18. http://dx.doi.org/10.1017/s1743921306004960.

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AbstractGalaxy bimodality is caused by the bulge-disc nature of galaxies as opposed to two distinct galaxy classes. This is evident in the colour-structure plane which clearly shows that elliptical galaxies (bulge-only) lie in the red compact peak and late-type spiral galaxies (disc-dominated) lie in the blue diffuse peak. Early-type spirals (bulge plus disc systems) sprawl across both peaks. However after bulge-disc decomposition the bulges of early-type spirals lie exclusively in the red compact peak and their discs in the blue diffuse peak (exceptions exist but are rare, e.g., dust reddened edge-on discs and blue pseudo-bulges). Movement between these two peaks is not trivial because whilst switching off star-formation can transform colours from blue to red, modifying the orbits of ~1 billion stars from a planar diffuse structure to a triaxial compact structure is problematic (essentially requiring an equal mass merger). We propose that the most plausible explanation for the dual structure of galaxies is that galaxy formation proceeds in two stages. First an initial collapse phase (forming a centrally concentrated core and black hole), followed by splashback, infall and accretion (forming a planar rotating disc). Dwarf systems coule perhaps follow the same scenario but the lack of low luminosity bulge-disc systems would imply that the two components must rapidly blend to form a single flattened spheroidal system.

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23

Conselice, Christopher J. "Galaxy bulges at mid- and high-redshift." Proceedings of the International Astronomical Union 3, S245 (July 2007): 429–38. http://dx.doi.org/10.1017/s1743921308018309.

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AbstractBulges are a major galaxy component in the nearby universe, and are one of the primary features that differentiates and defines galaxies. The origin of bulges can be directly probed in part by examining distant galaxies to search for high redshift bulges, and to study the properties of bulges in formation. We review the evidence for bulges at high redshift in this article, and how by studying bulges through a variety of approaches, including through morphological, colour, and stellar mass selection, we can determine when and how these systems assembled. We argue that the majority of the most massive ‘classical’ bulges are in place by z ~ 1.5 − 2, and likely formed very early through major mergers. Other, likely lower mass, bulges form through a secular process along with their disks. Direct observations suggest that these two formation processes are occurring, as spheroids are commonly seen at z < 1, as are disks and spiral galaxies in the form of luminous diffuse objects, clump-clusters, and chain galaxies. However, bulge+disk systems are relatively rare until z ~ 1, suggesting that this structural assembly occurred relatively late.

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Zaritsky, Dennis, Marcia Rieke, and Hans-Walter Rix. "IR imaging of spiral galaxy bulges." Symposium - International Astronomical Union 153 (1993): 441–42. http://dx.doi.org/10.1017/s0074180900123988.

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Imaging in the infrared (2.2μ) minimizes the impact of dust obscuration and allows reliable mapping of the mass-tracing stellar population in spiral galaxies. We find dramatic differences compared to photometry at shorter wavelengths (e.g. 0.8μ). As an example, the observations of the mini-bar and inner spiral arms of M 51 are discussed.

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Barway, Sudhanshu, Kaustubh Vaghmare, Smita Mathur, and Ajit Kembhavi. "A Spitzer Study of Pseudobulges in S0 Galaxies: Secular Evolution of Disks." Proceedings of the International Astronomical Union 11, S321 (March 2016): 299. http://dx.doi.org/10.1017/s1743921316011182.

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AbstractA comparison of pseudobulges in S0 and spiral galaxies is presented using structural parameters derived from 2-d decomposition of mid-infrared images taken at 3.6 μm by Spitzer IRAC. The position of the bulges on the Kormendy diagram has been used as an initial classification criterion for determining the nature of the bulge. To make the classification more secure, the criterion proposed by Fisher and Drory (2008) has also been used, which involves using the n = 2 division line on Sérsic index. We find that among the 185 S0 galaxies, 27 are pseudobulge hosts while 160 are classical. Of these 25 pseudobulge hosts, only two belong to the bright luminosity class (MK < 22.66, AB system) while rest belong to the faint luminosity class (MK > 22.66, AB system). We find that among spiral galaxies, 77 % (24 of 31) of the bulges are classified as pseudobulges. As pointed out by various studies, the presence of such a large fraction poses problems to our current picture of galaxy formation. How ever, our primary result is that the disk scale length of pseudobulge hosting S0s is significantly smaller on average than that of their spiral counterparts. This can be explained as a lowered disk luminosity which in turn implies that S0s have evolved from spiral progenitors. We also argue that early type spirals are more likely to be the progenitors based on bulge and total luminosity arguments. We speculate that if late type spirals hosting pseudobulges have to evolve into S0s, an additional mechanism along with gas stripping of spirals is needed. We have also investigated the effect of environment on pseudobulges in the two samples, but no significant trends were found in the properties of the pseudobulges as a function of the various structural parameters. The study is made more difficult because of the low number statistics one deals with when the sample is sub-divided based on whether it is in a field or group/cluster environment. The study of pseudobulges based on environment, however, is an interesting one and is something that can be considered for the future by carefully selecting a sample with statistically meaningful number of objects from diverse environments.

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Morelli, L., E. M. Corsini, A. Pizzella, E. Dalla Bontà, L. Coccato, J. Méndez-Abreu, and M. Cesetti. "Stellar populations of bulges in galaxies with a low surface-brightness disc." Proceedings of the International Astronomical Union 10, H16 (August 2012): 340. http://dx.doi.org/10.1017/s1743921314006048.

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AbstractThe radial profiles of the Hβ, Mg, and Fe line-strength indices are presented for a sample of eight spiral galaxies with a low surface-brightness stellar disc and a bulge. The correlations between the central values of the line-strength indices and velocity dispersion are consistent to those known for early-type galaxies and bulges of high surface-brightness galaxies. The age, metallicity, and α/Fe enhancement of the stellar populations in the bulge-dominated region are obtained using stellar population models with variable element abundance ratios. Almost all the sample bulges are characterized by a young stellar population, on-going star formation, and a solar α/Fe enhancement. Their metallicity spans from high to sub-solar values. No significant gradient in age and α/Fe enhancement is measured, whereas only in a few cases a negative metallicity gradient is found. These properties suggest that a pure dissipative collapse is not able to explain formation of all the sample bulges and that other phenomena, like mergers or acquisition events, need to be invoked. Such a picture is also supported by the lack of a correlation between the central value and gradient of the metallicity in bulges with very low metallicity. The stellar populations of the bulges hosted by low surface-brightness discs share many properties with those of high surface-brightness galaxies. Therefore, they are likely to have common formation scenarios and evolution histories. A strong interplay between bulges and discs is ruled out by the fact that in spite of being hosted by discs with extremely different properties, the bulges of low and high surface-brightness discs are remarkably similar.

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27

Bittner, A., D. A. Gadotti, B. G. Elmegreen, E. Athanassoula, D. M. Elmegreen, A. Bosma, and J. Muñoz-Mateos. "The sequence of spiral arm classes: Observational signatures of persistent spiral density waves in grand-design galaxies." Proceedings of the International Astronomical Union 14, S353 (June 2019): 140–43. http://dx.doi.org/10.1017/s1743921319008160.

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AbstractWe investigate how the properties of spiral arms relate to other fundamental galaxy properties. To this end, we use previously published measurements of those properties, and our own measurements of arm-interarm luminosity contrasts for a large sample of galaxies, using 3.6μm images from the Spitzer Survey of Stellar Structure in Galaxies. Flocculent galaxies are clearly distinguished from other spiral arm classes, especially by their lower stellar mass and surface density. Multi-armed and grand-design galaxies are similar in most of their fundamental parameters, excluding some bar properties and the bulge-to-total luminosity ratio. Based on these results, we discuss dense, classical bulges as a necessary condition for standing spiral wave modes in grand-design galaxies. We further find a strong correlation between bulge-to-total ratio and bar contrast, and a weaker correlation between arm and bar contrasts.

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Peletier, Reynier F., Katia Ganda, Jesús Falcón-Barroso, Roland Bacon, Michele Cappellari, Roger L. Davies, P. Tim de Zeeuw, et al. "Spiral galaxies in the SAURON survey." Proceedings of the International Astronomical Union 3, S245 (July 2007): 271–76. http://dx.doi.org/10.1017/s1743921308017894.

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AbstractWe discuss some recent integral field spectroscopy using the SAURON instrument of a sample consisting of 24 early-type spirals, part of the SAURON Survey, and 18 late-type spirals. Using 2-dimensional maps of their stellar radial velocity, velocity dispersion, and absorption line strength, it is now much easier to understand the nature of nearby galactic bulges. We discuss a few highlights of this work, and point out some new ideas about the formation of galactic bulges.

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29

Erwin, Peter, Roberto P. Saglia, Maximilian Fabricius, Jens Thomas, Nina Nowak, Stephanie Rusli, Ralf Bender, Juan Carlos Vega Beltrán, and John E. Beckman. "Composite bulges: the coexistence of classical bulges and discy pseudo-bulges in S0 and spiral galaxies." Monthly Notices of the Royal Astronomical Society 446, no. 4 (December 9, 2014): 4039–77. http://dx.doi.org/10.1093/mnras/stu2376.

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Johnston, Evelyn J., Alfonso Aragón-Salamanca, and Michael R. Merrifield. "Understanding the transformation of spirals to lenticulars." Proceedings of the International Astronomical Union 10, S309 (July 2014): 225–26. http://dx.doi.org/10.1017/s1743921314009739.

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AbstractBy studying the individual star-formation histories of the bulges and discs of lenticular (S0) galaxies, it is possible to build up a sequence of events that leads to the cessation of star formation and the consequent transformation from the progenitor spiral. In order to separate the bulge and disc stellar populations, we spectroscopically decomposed long-slit spectra of Virgo Cluster S0s into bulge and disc components. Analysis of the decomposed spectra shows that the most recent star formation activity in these galaxies occurred within the bulge regions, having been fuelled by residual gas from the disc. These results point towards a scenario where the star formation in the discs of spiral galaxies are quenched, followed by a final episode of star formation in the central regions from the gas that has been funnelled inwards through the disc.

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31

Botirov, Farkhod, and Salakhutdin Nuritdinov. "Nonlinear cosmogony of the spiral galaxy bulges." Open Astronomy 30, no. 1 (January 1, 2021): 144–48. http://dx.doi.org/10.1515/astro-2021-0019.

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Abstract In this paper, we develop an early idea of one of the authors (Nuritdinov 1992a,b), who was the first to propose the mechanism of instability of the warp perturbation mode on the background of a nonstationary disk. For this aim, we have studied a model of a nonlinearly non-stationary self-gravitating disk with an anisotropic velocity diagram. The model has a composite nature, or rather, it is a superposition of isotropic and anisotropic states of the disk. In the general case, it is obtained a nonstationary analogue of the dispersion equation of this composite model. We have also investigated the behavior of the domed perturbation mode, the instability of which leads to the formation of a classical bulge in the central region of the disk. In addition, we considered the critical diagrams of the dependence of the virial ratio on the rotation rate of the system for various values of the superposition parameter and the corresponding diagrams for the increments of instability.

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32

Batcheldor, D., D. Axon, D. Merritt, M. A. Hughes, A. Marconi, J. Binney, A. Capetti, M. Merrifield, C. Scarlata, and W. Sparks. "Integral Field Spectroscopy of 23 Spiral Bulges." Astrophysical Journal Supplement Series 160, no. 1 (September 2005): 76–86. http://dx.doi.org/10.1086/431483.

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33

Moorthy, B. K., and J. A. Holtzman. "Stellar populations in bulges of spiral galaxies." Monthly Notices of the Royal Astronomical Society 371, no. 2 (September 11, 2006): 583–608. http://dx.doi.org/10.1111/j.1365-2966.2006.10722.x.

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34

Pfenniger, D. "Stellar Dynamics and the 3D Structure of Bars." International Astronomical Union Colloquium 157 (1996): 273–85. http://dx.doi.org/10.1017/s0252921100049915.

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AbstractRecent observational constraints restrict the strict applicability of stellar dynamics in spirals to a few rotation periods. However, stellar dynamics concepts such as periodic orbits are invaluable for understanding the various dynamical processes occurring during much more periods. A distinction of two instability types in stellar systems is pointed out, the first one being well illustrated by the bar instability, and the second one by the bar bending instability. In bars the third dimension brings essential dynamical effects which modify the views about the history of bulges and the spiral secular evolution. Bars may grow, bend, thicken, and dissolve into spheroidal bulges, and spirals may evolve along the Hubble sequence in the sense Sd→Sa. This leads to a much more dynamical picture of isolated galaxies than imagined before.

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35

Kim, E., S. S. Kim, G. H. Lee, M. G. Lee, and R. de Grijs. "Gas inflow and nuclear star formation in galaxies with non-axisymmetric bulges." Proceedings of the International Astronomical Union 9, S303 (October 2013): 171–73. http://dx.doi.org/10.1017/s1743921314000477.

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AbstractWe present the dependence of the amount of nuclear star formation on the non-axisymmetry of a bulge of disk galaxies. For this, we use a volume-limited sample of spiral galaxies at 0.02 < = z < 0.055 from the SDSS DR7. Among 3173 final sample galaxies with an axis ratio b/a > 0.6 and a bulge fraction ranged in B/T <= 0.41, nuclear starburst galaxies are 10%. We find that a fraction of the nuclear starburst galaxies become higher when ellipticity of a bulge increases in early type galaxies. Also, the fraction increases clearly when early type galaxies are isolated and in low density region. Our results indicate that the non-axisymmetry of bulges assists gas to fall inside and affects the nuclear starburst process in disk galaxies.

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36

Reshetnikov, V. P. "On the photometric characteristics of ellipticals and bulges of spirals in interacting systems." Symposium - International Astronomical Union 153 (1993): 419–20. http://dx.doi.org/10.1017/s0074180900123873.

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37

Pastrav, Bogdan A., Cristina C. Popescu, Richard J. Tuffs, and Anne E. Sansom. "Dust effects on the derived Sérsic indexes of disks and bulges in spiral galaxies." Proceedings of the International Astronomical Union 7, S284 (September 2011): 306–8. http://dx.doi.org/10.1017/s1743921312009313.

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AbstractWe present a theoretical study that quantifies the effect of dust on the derived Sérsic indexes of disks and bulges. The changes in the derived parameters from their intrinsic values (as seen in the absence of dust) were obtained by fitting Sérsic distributions on simulated images of disks and bulges produced using radiative transfer calculations and the model of Popescu et al. (2011). We found that dust has the effect of lowering the measured Sérsic index in most cases, with stronger effects for disks and bulges seen through more optically thick lines of sight.

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38

Domínguez-Tenreiro, R., F. J. Martínez-Serrano, A. Serna, M. Mollá, and J. Oñorbe. "Bulges vs elliptical galaxies: some clues from their formation in a cosmological context." Proceedings of the International Astronomical Union 3, S245 (July 2007): 71–74. http://dx.doi.org/10.1017/s1743921308017316.

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AbstractWe report on an extension, through cosmological simulations, of the two-phase formation scenario for elliptical galaxies to classical spiral bulges. In particular, we analyze the possibility that the old stellar population of bulges forms in a fast phase, while the younger stellar component forms or is assembled in a slow phase, in part from disk material suffering instabilities and in part through satellite capture or mergers.

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39

Zaritsky, D., and K. Y. Lo. "Evidence for nonaxisymmetric nuclear bulges in spiral galaxies." Astrophysical Journal 303 (April 1986): 66. http://dx.doi.org/10.1086/164052.

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40

Proctor, R. N., A. E. Sansom, and I. N. Reid. "Constraining the star formation histories of spiral bulges." Monthly Notices of the Royal Astronomical Society 311, no. 1 (January 1, 2000): 37–49. http://dx.doi.org/10.1046/j.1365-8711.2000.03018.x.

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41

Chenko, O. K. Sil'. "Abundance jump in the inner bulges of galaxies." Symposium - International Astronomical Union 153 (1993): 427–28. http://dx.doi.org/10.1017/s0074180900123915.

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42

Jablonka, P., P. Martin, and N. Arimoto. "The Luminosity-Metallicity Relation for Bulges of Spiral Galaxies." Astronomical Journal 112 (October 1996): 1415. http://dx.doi.org/10.1086/118109.

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43

Graham, Alister W. "An Investigation into the Prominence of Spiral Galaxy Bulges." Astronomical Journal 121, no. 2 (February 2001): 820–40. http://dx.doi.org/10.1086/318767.

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44

Morelli, L., A. Pizzella, E. M. Corsini, E. Dalla Bontà, L. Coccato, J. Méndez-Abreu, and M. Parmiggiani. "Stellar populations of the bulges of four spiral galaxies." Astronomische Nachrichten 336, no. 2 (March 2015): 208–19. http://dx.doi.org/10.1002/asna.201412155.

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45

Pastrav, B. A., C. C. Popescu, R. J. Tuffs, and A. E. Sansom. "The effects of dust on the derived photometric parameters of disks and bulges in spiral galaxies." Proceedings of the International Astronomical Union 8, S292 (August 2012): 290. http://dx.doi.org/10.1017/s1743921313001440.

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AbstractHere we present results on the effects of dust on the derived Sérsic index of disks and bulges. This is part of a larger study (see Pastrav et al. 2012a, Pastrav et al. 2012b) that quantifies the dust effects on all photometric parameters, including scale-lengths, axis-ratios, central surface brightness and effective radii of individual and decomposed (from B/D decomposition) disks and bulges. The effects of dust are derived for both broadband and narrow line (Balmer lines) images. The changes in the derived photometric parameters from their intrinsic values (as seen in the absence of dust) were obtained by fitting simulated images of disks and bulges produced using radiative transfer calculations and the model of Popescu et al. (2011). This study follows on the analysis of Möllenhoff et al. (2006), who quantified the effects of dust on the photometry of old stellar disks seen at low and intermediate inclination. We extend the study to disks at all inclinations and we investigate the changes in the photometry of young stellar disks and bulges. For the individual components, in the majority of cases: 1) the dust lowers the Sérsic index from its intrinsic value; 2) the Sérsic index decreases as the inclination and the B band central face-on dust opacity, τBf, increase. For the decomposed disks and bulges, dust slightly increases the Sérsic index as compared with the one derived on individual components (e.g. Fig. 1); this effect is stronger for higher values of the inclination, τBf and B/D.

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46

Kormendy, John. "Kinematics of extragalactic bulges: evidence that some bulges are really disks." Symposium - International Astronomical Union 153 (1993): 209–30. http://dx.doi.org/10.1017/s0074180900123204.

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Recent work on the dynamics of galaxy bulges has been dominated by two themes. (1) Bulges share the richness in kinematic structure that is currently being discovered in elliptical galaxies. This includes kinematic evidence for triaxiality and for accretion (counterrotating gas and stellar components). (2) The main subject of this paper is observational and theoretical evidence that some “bulges” are built secularly out of disk material. Many bulges show photometric and kinematic evidence for disklike dynamics. This includes (i) velocity dispersions σ much smaller than those predicted by the Faber-Jackson σ — MB correlation, (ii) rapid rotation V(r) that implies V/σ values well above the “oblate line” describing rotationally flattened, isotropic spheroids in the V/σ — ellipticity diagram, and (iii) spiral structure dominating the r1/4 part of the galaxy. In these galaxies, the steep, r1/4-law central brightness profiles belong not to bulges but to disks. That is, some galaxy disks have central brightness profiles that are much steeper than the inward extrapolation of an exponential fit to the outer parts. These observations and n-body simulations of gas flow in nonaxisymmetric galaxies imply that high-central-concentration, flat components can be formed out of disk gas that is transported toward the center by bars and oval distortions. The n-body models suggest further that some “bulges” are built of disk stars heated in the axial direction by resonant scattering off of bars. These effects are signs that important secular evolution processes are at work in galaxy disks.

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47

Breda, Iris, Polychronis Papaderos, and Jean-Michel Gomes. "Indications of the invalidity of the exponentiality of the disk within bulges of spiral galaxies." Astronomy & Astrophysics 640 (August 2020): A20. http://dx.doi.org/10.1051/0004-6361/202037889.

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Context. A fundamental subject in extragalactic astronomy concerns the formation and evolution of late-type galaxies (LTGs). The standard scenario envisages a two-phase build-up for these systems, comprising the early assembly of the bulge followed by disk accretion. However, recent observational evidence points to a joint formation and perpetual coevolution of these structural components. Our current knowledge on the properties of the bulge and the disk is, to a large degree, founded on photometric decomposition studies, which sensitively depend on the adopted methodology and enclosed assumptions on the structure of LTGs. A critical assumption whose validity had never been questioned before is that galactic disks conserve their exponential nature up to the galactic center. This, although seemingly plausible, implies that bulge and disk coexist without significant dynamical interaction and mass exchange over nearly the entire Hubble time. Aims. Our goal is to examine the validity of the standard assumption that galactic disks preserve their exponential intensity profile inside the bulge radius (RB) all the way to the galactic center, as is generally assumed in photometric decomposition studies. Methods. We developed a spectrophotometric bulge-disk decomposition technique that provides an estimation for the net (i.e., disk-subtracted) spectrum of the bulge. Starting from an integral field spectroscopy (IFS) data cube, this tool computes the integrated spectrum of the bulge and the disk, scales the latter considering the light fraction estimated from photometric decomposition techniques, and subtract it from the former, thereby allowing for the extraction of the net-bulge spectrum. Considering that the latter depends on the underlying assumption for the disk luminosity profile, checking its physical plausibility (for instance, positiveness and spectral slope) places indirect constraints on the validity of the disk’s assumed profile inside the radius R⋆ < RB. In this pilot study, we tested the following three different disk configurations: the standard exponential disk profile as well as a centrally flattened or down-bending exponential disk profile. Results. A systematic application of our spectrophotometric bulge-disk decomposition tool to a representative sample of 135 local LTGs from the CALIFA survey yields a significant fraction (up to ∼30 (20)%) of unphysical net-bulge spectra when a purely exponential (centrally flattened) intensity profile is assumed for the disk. This never occurs for disks’ profiles involving a centrally decreasing intensity. Conclusions. The obtained results suggest that, for a significant fraction of LTGs, the disk component shows a down-bending beneath the bulge. If proven to be true, this result will call for a substantial revision of structural decomposition studies for LTGs and it will have far-reaching implications in our understanding of the photometric properties of their bulges. Given its major relevance, it appears worthwhile to explore the central stellar surface density of galactic disks further, through an improved version of the spectrophotometric decomposition tool presented here and its application combining deep surface photometry, spatially resolved spectral synthesis, and kinematical analyses.

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48

Bureau, M., and K. C. Freeman. "The Nature of Boxy/Peanut-Shaped Bulges in Spiral Galaxies." Astronomical Journal 118, no. 1 (July 1999): 126–38. http://dx.doi.org/10.1086/300922.

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49

Saha, Kanak, and Bruce Elmegreen. "LONG-LIVED SPIRAL STRUCTURE FOR GALAXIES WITH INTERMEDIATE-SIZE BULGES." Astrophysical Journal 826, no. 2 (July 25, 2016): L21. http://dx.doi.org/10.3847/2041-8205/826/2/l21.

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50

Hughes, Mark A., Almudena Alonso-Herrero, John Atkinson, David J. Axon, Dan Batcheldor, C. Marcella Carollo, Alessandro Marconi, and Claudia Scarlata. "Nuclear clusters, bulges and massive black holes in spiral galaxies." Proceedings of the International Astronomical Union 2004, IAUS222 (March 2004): 181–82. http://dx.doi.org/10.1017/s1743921304001942.

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