We present a new morphological indicator designed for automated recognition of galaxies with faint asymmetric tidal features suggestive of an ongoing or past merger. We use the new indicator, ...together with pre-existing diagnostics of galaxy structure to study the role of galaxy mergers in inducing (post-) starburst spectral signatures in local galaxies, and investigate whether (post-) starburst galaxies play a role in the build-up of the ‘red sequence’. Our morphological and structural analysis of an evolutionary sample of 335 (post-) starburst galaxies in the Sloan Digital Sky Survey DR7 with starburst ages 0 < t
SB < 0.6 Gyr, shows that 45 per cent of galaxies with young starbursts (t
SB < 0.1 Gyr) show signatures of an ongoing or past merger. This fraction declines with starburst age, and we find a good agreement between automated and visual classifications. The majority of the oldest (post-) starburst galaxies in our sample (t
SB ∼ 0.6 Gyr) have structural properties characteristic of early-type discs and are not as highly concentrated as the fully quenched galaxies commonly found on the ‘red sequence’ in the present day Universe. This suggests that, if (post-) starburst galaxies are a transition phase between active star-formation and quiescence, they do not attain the structure of presently quenched galaxies within the first 0.6 Gyr after the starburst.
Context.
The cosmic evolution of the barred galaxy population provides key information about the secular evolution of galaxies and the settling of rotationally dominated discs.
Aims.
We study the bar ...fraction in the SMACSJ0723.37323 (SMACS0723) cluster of galaxies at
z
= 0.39 using the Early Release Observations obtained with the NIRCam instrument mounted on the JWST telescope.
Methods.
We visually inspected all cluster member galaxies using the images from the NIRCam
F
200
W
filter. We classified the galaxies into ellipticals and discs and determine the presence of a bar. The cluster member selection was based on a combined method using both the available spectroscopy and the color-magnitude relation.
Results.
As has previously been found in nearby galaxy samples, we find that the bar fraction distribution of SMACS0723 is a strong function of the galaxy stellar luminosity (or stellar mass). The analogy with local clusters, such as Virgo and Coma, reveals a similar distribution among the three clusters for low-mass galaxies (log(
M
⋆
/
M
⊙
)≤9.5). The comparison with a sample of local galaxies in a field environment shows a remarkable lack of bars in this low-mass regime for the SMACS0723 cluster (and, therefore, in Virgo and Coma) with respect to the field. At high masses (log(
M
⋆
/
M
⊙
)≥10.25), galaxies in SMACS0723 show a slightly lower bar fraction than those in Coma. At these high masses, we find a much larger bar fraction in SMACS0723 than previous works on field galaxies at
z
∼ 0.4. Nevertheless, the difference is only marginal when we compare with a sample of well-resolved local field galaxies. Thus, we suggest that the improved capabilities of JWST with respect to HST in terms of both spatial resolution and image depth are responsible for the higher bar fraction we obtained.
Conclusions.
Our results support a scenario where cluster environment affects the formation of bars in a mass-dependent way. At high masses, the mild increase in the bar fraction of local clusters (Coma) with respect to both SMACS0723 and local field galaxies suggests a weak effect coming from the cluster environment possibly triggering bar formation. On the other hand, low-mass galaxies show the same bar fraction in the three clusters (different redshifts) and a significant drop with respect to field galaxies at
z
= 0, thus suggesting that: (i) the bar fraction of low-mass galaxies in clusters is not evolving during the last 4 Gyr; and (ii) bar formation is severely inhibited in low-mass galaxies residing in clusters.
Context. Historically, galaxy bulges were thought to be single-component objects at the center of galaxies. However, this picture is now questioned since different bulge types with different ...formation paths, namely classical and pseudobulges, have been found coexisting within the same galaxy. Aims. We study the incidence and nature of composite bulges in a sample of 10 face-on barred galaxies to constrain the formation and evolutionary processes of the central regions of disk galaxies. Methods. We analyze the morphological, photometric, and kinematic properties of each bulge. Then, by using a case-by-case analysis we identify composite bulges and classify every component into a classical or pseudobulge. In addition, bar-related boxy/peanut (B/P) structures were also identified and characterized. Results. We find only three galaxies hosting a single-component bulge (two pseudobulges and one classical bulge). Thus, we demonstrate the high incidence of composite bulges (70%) in barred galaxies. We find evidence of composite bulges coming in two main types based on their formation: secular-built and merger- and secular-built. We denote as secular-built those composite bulges that are made up of structures associated with secular processes, such as pseudobulges, central disks, or B/P bulges. We find four composite bulges of this kind in our sample. On the other hand, merger- and secular-built bulges are those where structures with different formation paths coexist within the same galaxy, i.e., a classical bulge coexisting with a secular-built structure (pseudobulge, central disk, or B/P). Three bulges of this kind were found in the sample. We notice the importance of detecting kinematic structures such as σ-drops to identify composite bulges. A high percentage (~80%) of galaxies were found to host σ-drops or σ-plateaus in our sample, revealing their high incidence in barred galaxies. Conclusions. The high frequency of composite bulges in barred galaxies points toward a complex formation and evolutionary scenario. Moreover, the evidence of coexisting merger- and secular-built bulges reinforce this idea. We discuss how the presence of different bulge types with different formation histories and timescales can constrain current models of bulge formation.
Abstract
Post-starburst galaxies can be identified via the presence of prominent Hydrogen Balmer absorption lines in their spectra. We present a comprehensive study of the origin of strong Balmer ...lines in a volume-limited sample of 189 galaxies with 0.01 < z < 0.05, $\log ({\it M}_{\star }/{\it M}_{{\odot }})>9.5$ and projected axial ratio b/a > 0.32. We explore their structural properties, environments, emission lines, and star formation histories, and compare them to control samples of star-forming and quiescent galaxies, and simulated galaxy mergers. Excluding contaminants, in which the strong Balmer lines are most likely caused by dust-star geometry, we find evidence for three different pathways through the post-starburst phase, with most events occurring in intermediate-density environments: (1) a significant disruptive event, such as a gas-rich major merger, causing a starburst and growth of a spheroidal component, followed by quenching of the star formation (70 per cent of post-starburst galaxies at $9.5<\log (\mbox{{$M$}}_{\star }/\mbox{{$M$}}_{{\odot }})<10.5$ and 60 per cent at $\log (\mbox{{$M$}}_{\star }/\mbox{{$M$}}_{{\odot }})>10.5$); (2) at $9.5<\log (\mbox{{$M$}}_{\star }/\mbox{{$M$}}_{{\odot }})<10.5$, stochastic star formation in blue-sequence galaxies, causing a weak burst and subsequent return to the blue sequence (30 per cent); (3) at $\log (\mbox{{$M$}}_{\star }/\mbox{{$M$}}_{{\odot }})>10.5$, cyclic evolution of quiescent galaxies which gradually move towards the high-mass end of the red sequence through weak starbursts, possibly as a result of a merger with a smaller gas-rich companion (40 per cent). Our analysis suggests that active galactic nuclei (AGNs) are ‘on’ for $50\hbox{ per cent}$ of the duration of the post-starburst phase, meaning that traditional samples of post-starburst galaxies with strict emission-line cuts will be at least $50\hbox{ per cent}$ incomplete due to the exclusion of narrow-line AGNs.
We present the stellar kinematic maps of a large sample of galaxies from the integral-field spectroscopic survey CALIFA. The sample comprises 300 galaxies displaying a wide range of morphologies ...across the Hubble sequence, from ellipticals to late-type spirals. This dataset allows us to homogeneously extract stellar kinematics up to several effective radii. In this paper, we describe the level of completeness of this subset of galaxies withrespect to the full CALIFA sample, as well as the virtues and limitations of the kinematic extraction compared to other well-known integral-field surveys. In addition, we provide averaged integrated velocity dispersion radial profiles for different galaxy types, which are particularly useful to apply aperture corrections for single aperture measurements or poorly resolved stellar kinematics of high-redshift sources. The work presented in this paper sets the basis for the study of more general properties of galaxies that will be explored in subsequent papers of the survey.
We present a convenient, all-in-one framework for the scientific analysis of fully reduced, (integral-field) spectroscopic data. The Galaxy IFU Spectroscopy Tool (GIST) is entirely written in Python ...3 and conducts all the steps from the preparation of input data to the scientific analysis and to the production of publication-quality plots. In its basic set-up, it extracts stellar kinematics, performs an emission-line analysis, and derives stellar population properties from full spectral fitting and via the measurement of absorption line-strength indices by exploiting the well-known pPXF and GandALF routines, where the latter has now been implemented in Python. The pipeline is not specific to any instrument or analysis technique and provides easy means of modification and further development, thanks to its modular code architecture. An elaborate, Python-native parallelisation is implemented and tested on various machines. The software further features a dedicated visualisation routine with a sophisticated graphical user interface. This allows an easy, fully interactive plotting of all measurements, spectra, fits, and residuals, as well as star formation histories and the weight distribution of the models. The pipeline has been successfully applied to both low- and high-redshift data from MUSE, PPAK (CALIFA), and SINFONI, and to simulated data for HARMONI and WEAVE and is currently being used by the TIMER, Fornax3D, and PHANGS collaborations. We demonstrate its capabilities by applying it to MUSE TIMER observations of NGC 1433.
We present photometry and long-slit spectroscopy for 12 S0 and spiral galaxies selected from the Catalogue of Isolated Galaxies. The structural parameters of the sample galaxies are derived from the ...Sloan Digital Sky Survey i-band images by performing a two-dimensional photometric decomposition of the surface brightness distribution. This is assumed to be the sum of the contribution of a Sersic bulge, an exponential disc, and a Ferrers bar characterized by elliptical and concentric isophotes with constant ellipticity and position angles. The rotation curves and velocity dispersion profiles of the stellar component are measured from the spectra obtained along the major axis of galaxies. The radial profiles of the H..., Mg and Fe line-strength indices are derived too. Correlations between the central values of the Mg sub( 2) and ...Fe... line-strength indices and the velocity dispersion are found. The mean age, total metallicity and total .../Fe enhancement of the stellar population in the centre and at the radius, where the bulge gives the same contribution to the total surface brightness as the remaining components, are obtained using stellar population models with variable element abundance ratios. We identify intermediate-age bulges with solar metallicity and old bulges with a large spread in metallicity. Most of the sample bulges display supersolar .../Fe enhancement, no gradient in age and negative gradients of metallicity and .../Fe enhancement. These findings support a formation scenario via dissipative collapse where environmental effects are remarkably less important than in the assembly of bulges of galaxies in groups and clusters. (ProQuest: ... denotes formulae/symbols omitted.)
ABSTRACT
This series of papers aims at understanding the formation and evolution of non-barred disc galaxies. We use the new spectro-photometric decomposition code, c2d, to separate the spectral ...information of bulges and discs of a statistically representative sample of galaxies from the CALIFA survey. Then, we study their stellar population properties analysing the structure-independent datacubes with the Pipe3D algorithm. We find a correlation between the bulge-to-total (B/T) luminosity (and mass) ratio and galaxy stellar mass. The B/T mass ratio has only a mild evolution with redshift, but the bulge-to-disc (B/D) mass ratio shows a clear increase of the disc component since redshift z < 1 for massive galaxies. The mass–size relation for both bulges and discs describes an upturn at high galaxy stellar masses (log (M⋆/M⊙) > 10.5). The relation holds for bulges but not for discs when using their individual stellar masses. We find a negligible evolution of the mass–size relation for both the most massive ($\log {(M_{\star \rm ,b,d}/{\rm M}_{\odot })} \gt 10$) bulges and discs. For lower masses, discs show a larger variation than bulges. We also find a correlation between the Sérsic index of bulges and both galaxy and bulge stellar mass, which does not hold for the disc mass. Our results support an inside-out formation of nearby non-barred galaxies, and they suggest that (i) bulges formed early-on and (ii) they have not evolved much through cosmic time. However, we find that the early properties of bulges drive the future evolution of the galaxy as a whole, and particularly the properties of the discs that eventually form around them.
We investigate the role of stellar mass in shaping the intrinsic thickness of galaxy discs by determining the probability distribution of apparent axial ratios (b/a) for two different samples that ...probe the faint end of the galaxy luminosity function. We find that the b/a distribution has a characteristic ‘U-shape’ and identify a limiting mass M*≈ 2 × 109M⊙ below which low-mass galaxies start to be systematically thicker. This tendency holds for very faint (MB∼−8) dwarfs in the local volume, which are essentially spheroidal systems. We argue that galaxy shape is the result of the complex interplay between mass, specific angular momentum and stellar feedback effects. Thus, the increasing importance of turbulent motions in lower mass galaxies leads to the formation of thicker systems, a result supported by the latest hydrodynamical simulations of dwarf galaxy formation and other theoretical expectations. We discuss several implications of this finding, including the formation of bars in faint galaxies, the deprojection of Hi line profiles and simulations of environmental effects on the dwarf galaxy population.
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