ABSTRACT
Variations of the stellar initial mass function (IMF) in external galaxies have been inferred from a variety of independent probes. Yet the physical conditions causing these variations ...remain largely unknown. In this work, we explore new spatially resolved measurements of the IMF for three edge-on lenticular galaxies in the Fornax cluster. We utilize existing orbit-based dynamical models in order to fit the new IMF maps within an orbital framework. We find that, within each galaxy, the high-angular momentum disc-like stars exhibit an IMF which is rich in dwarf stars. The centrally concentrated pressure-supported orbits exhibit similarly dwarf-rich IMF. Conversely, orbits at large radius which have intermediate angular momentum exhibit IMF which are markedly less dwarf-rich relative to the other regions of the same galaxy. Assuming that the stars which reside, in the present-day, on dynamically hot orbits at large radii are dominated by accreted populations, we interpret these findings as a correlation between the dwarf-richness of a population of stars, and the mass of the host in which it formed. Specifically, deeper gravitational potentials would produce more dwarf-rich populations, resulting in the relative deficiency of dwarf stars which originated in the lower mass accreted satellites. The central and high-angular momentum populations are likely dominated by in situ stars, which were formed in the more massive host itself. There are also global differences between the three galaxies studied here, of up to ∼0.3 dex in the IMF parameter ξ. We find no local dynamical or chemical property which alone can fully account for the IMF variations.
We introduce BAYES-LOSVD, a novel implementation of the non-parametric extraction of line-of-sight velocity distributions (LOSVDs) in galaxies. We employed Bayesian inference to obtain robust LOSVDs ...and associated uncertainties. Our method relies on a principal component analysis to reduce the dimensionality on the set of templates required for the extraction and thus increase the performance of the code. In addition, we implemented several options to regularise the output solutions. Our tests, conducted on mock spectra, confirm the ability of our approach to model a wide range of LOSVD shapes, overcoming limitations of the most widely used parametric methods (e.g., Gauss-Hermite expansion). We present examples of LOSVD extractions for real galaxies with known peculiar LOSVD shapes, including
NGC 4371
,
IC 0719
, and
NGC 4550
, using MUSE and
SAURON
integral-field unit (IFU) data. Our implementation can also handle data from other popular IFU surveys (e.g.,
ATLAS
3D
,
CALIFA
,
MaNGA
,
SAMI
).
We place our sample of 18 Virgo dwarf early-type galaxies (dEs) on the (V - K)(e)-velocity dispersion, Faber-Jackson, and fundamental plane (FP) scaling relations for massive early-type galaxies ...(Es). We use a generalized velocity dispersion, which includes rotation, to be able to compare the location of both rotationally and pressure supported dEs with those of early and late-type galaxies. We find that dEs seem to bend the Faber-Jackson relation of Es to lower velocity dispersions, being the link between Es and dwarf spheroidal galaxies (dSphs). Regarding the FP relation, we find that dEs are significantly offset with respect to massive hot stellar systems, and re-casting the FP into the so-called.-space suggests that this offset is related to dEs having a total mass-to-light ratio higher than Es but still significantly lower than dSph galaxies. Given a stellar mass-to-light ratio based on the measured line indices of dEs, the FP offset allows us to infer that the dark matter fraction within the half light radii of dEs is on average greater than or similar to 42% (uncertainties of 17% in the K band and 20% in the V band), fully consistent with an independent estimate in an earlier paper in this series. We also find that dEs in the size-luminosity relation in the near-infrared, like in the optical, are offset from early-type galaxies, but seem to be consistent with late-type galaxies. We thus conclude that the scaling relations show that dEs are different from Es, and that they further strengthen our previous findings that dEs are closer to and likely formed from late-type galaxies.
Extragalactic planetary nebulae (PNe) are detectable through relatively strong nebulous O
III
emission and act as direct probes into the local stellar population. Because they have an apparently ...universal invariant magnitude cut-off, PNe are also considered to be a remarkable standard candle for distance estimation. Through detecting PNe within the galaxies, we aim to connect the relative abundances of PNe to the properties of their host galaxy stellar population. By removing the stellar background components from FCC 167 and FCC 219, we aim to produce PN luminosity functions (PNLF) of these galaxies, and thereby also estimate the distance modulus to these two systems. Finally, we test the reliability and robustness of our novel detection and analysis method. It detects unresolved point sources by their O
III
5007 Å emission within regions that have previously been unexplored. We model the O
III
emissions in the spatial and spectral dimensions together, as afforded to us by the Multi Unit Spectroscopic Explorer, and we draw on data gathered as part of the Fornax3D survey. For each source, we inspect the properties of the nebular emission lines to remove other sources that might hinder the safe construction of the PNLF, such as supernova remnants and H
II
regions. As a further step, we characterise any potential limitations and draw conclusions about the reliability of our modelling approach through a set of simulations. By applying this novel detection and modelling approach to integral field unit observations, we report for the distance estimates and luminosity-specific PNe frequency values for the two galaxies. Furthermore, we include an overview of source contamination, galaxy differences, and possible effects on the PNe populations in the dense stellar environments.
ABSTRACT
We study the evolution of kinematically defined stellar discs in 10 Fornax-like clusters identified in the TNG50 run from the IllustrisTNG suite of cosmological simulations. We considered ...disc galaxies with present-day stellar mass M⋆ ≥ 3 × 108 M⊙ and follow their evolution since first entering their host cluster. Very few stellar discs survive since falling in such dense environments, ranging from 40 per cent surviving to all being disrupted. Such survival rates are consistent with what reported earlier for the two more massive, Virgo-like clusters in TNG50. In absolute terms, however, the low number of present-day disc galaxies in Fornax-like clusters could be at odds with the presence of three edge-on disc galaxies in the central regions of the actual Fornax cluster, as delineated by the Fornax3D survey. When looking at the Fornax analogues from random directions and with the same selection function of Fornax3D, the probability of finding three edge-on disc galaxies in any one Fornax-like cluster in TNG50 is rather low, albeit not impossible. We also compared the stellar-population properties near the equatorial plane derived from integral-field spectroscopy for the three edge-ons in Fornax to similar line-of-sight integrated values for present-day disc galaxies in TNG50. For one of these, the very old and metal-rich stellar population of its disc cannot be matched by any the disc galaxies in TNG50, including objects in the field. We discuss possible interpretations of these findings, while pointing to future studies on passive cluster spirals as a way to further test state-of-the-art cosmological simulations.
We present the second data release (DR2) of the X-shooter Spectral Library (XSL), which contains all the spectra obtained over the six semesters of that program. This release supersedes our first ...data release from Chen et al. (2014, A&A, 565, A117), with a larger number of spectra (813 observations of 666 stars) and with a more extended wavelength coverage as the data from the near-infrared arm of the X-shooter spectrograph are now included. The DR2 spectra then consist of three segments that were observed simultaneously and, if combined, cover the range between ∼300 nm and ∼2.45
μ
m at a spectral resolving power close to
R
= 10 000. The spectra were corrected for instrument transmission and telluric absorption, and they were also corrected for wavelength-dependent flux-losses in 85% of the cases. On average, synthesized broad-band colors agree with those of the MILES library and of the combined IRTF and Extended IRTF libraries to within ∼1%. The scatter in these comparisons indicates typical errors on individual colors in the XSL of 2−4%. The comparison with 2MASS point source photometry shows systematics of up to 5% in some colors, which we attribute mostly to zero-point or transmission curve errors and a scatter that is consistent with the above uncertainty estimates. The final spectra were corrected for radial velocity and are provided in the rest-frame (with wavelengths in air). The spectra cover a large range of spectral types and chemical compositions (with an emphasis on the red giant branch), which makes this library an asset when creating stellar population synthesis models or for the validation of near-ultraviolet to near-infrared theoretical stellar spectra across the Hertzsprung-Russell diagram.
We estimate the current extinction-corrected H star formation rate (SFR) of the different morphological components that shape galaxies (bulges, bars, and disks). We use a multicomponent photometric ...decomposition based on Sloan Digital Sky Survey imaging to Calar Alto Legacy Integral Field Area Integral Field Spectroscopy (IFS) datacubes for a sample of 219 galaxies. This analysis reveals an enhancement of the central SFR and specific SFR (sSFR = SFR/M ) in barred galaxies. Along the main sequence, we find that more massive galaxies in total have undergone efficient suppression (quenching) of their star formation, in agreement with many studies. We discover that more massive disks have had their star formation quenched as well. We evaluate which mechanisms might be responsible for this quenching process. The presence of type 2 AGNs plays a role at damping the sSFR in bulges and less efficiently in disks. Also, the decrease in the sSFR of the disk component becomes more noticeable for stellar masses around for bulges, it is already present at . The analysis of the line-of-sight stellar velocity dispersions ( ) for the bulge component and of the corresponding Faber-Jackson relation shows that AGNs tend to have slightly higher values than star-forming galaxies for the same mass. Finally, the impact of environment is evaluated by means of the projected galaxy density, 5. We find that the SFR of both bulges and disks decreases in intermediate- to high-density environments. This work reflects the potential of combining IFS data with 2D multicomponent decompositions to shed light on the processes that regulate the SFR.
Context. According to numerical simulations, stars are not always kept at their birth galactocentric distances but they have a tendency to migrate. The importance of this radial migration in shaping ...galactic light distributions is still unclear. However, if radial migration is indeed important, galaxies with different surface brightness (SB) profiles must display differences in their stellar population properties. Aims. We investigate the role of radial migration in the light distribution and radial stellar content by comparing the inner colour, age, and metallicity gradients for galaxies with different SB profiles. We define these inner parts, avoiding the bulge and bar regions and up to around three disc scale lengths (type I, pure exponential) or the break radius (type II, downbending; type III, upbending). Methods. We analysed 214 spiral galaxies from the CALIFA survey covering different SB profiles. We made use of GASP2D and SDSS data to characterise the light distribution and obtain colour profiles of these spiral galaxies. The stellar age and metallicity profiles were computed using a methodology based on full-spectrum fitting techniques (pPXF, GANDALF, and STECKMAP) to the Integral Field Spectroscopic CALIFA data. Results. The distributions of the colour, stellar age, and stellar metallicity gradients in the inner parts for galaxies displaying different SB profiles are unalike as suggested by Kolmogorov-Smirnov and Anderson-Darling tests. We find a trend in which type II galaxies show the steepest profiles of all, type III show the shallowest, and type I display an intermediate behaviour. Conclusions. These results are consistent with a scenario in which radial migration is more efficient for type III galaxies than for type I systems, where type II galaxies present the lowest radial migration efficiency. In such a scenario, radial migration mixes the stellar content, thereby flattening the radial stellar properties and shaping different SB profiles. However, in light of these results we cannot further quantify the importance of radial migration in shaping spiral galaxies, and other processes, such as recent star formation or satellite accretion, might play a role.
ABSTRACT
Using new long-slit spectroscopy obtained with X-Shooter at ESO-VLT, we study, for the first time, radial gradients of optical and near-infrared initial mass function (IMF)-sensitive ...features in a representative sample of galaxies at the very high mass end of the galaxy population. The sample consists of seven early-type galaxies (ETGs) at z ∼ 0.05, with central velocity dispersion in the range 300 ≲ σ ≲ 350 km s−1. Using state-of-the-art stellar population synthesis models, we fit a number of spectral indices, from different chemical species (including TiO and Na indices), to constrain the IMF slope (i.e. the fraction of low-mass stars), as a function of galactocentric distance, over a radial range out to ∼4 kpc. ETGs in our sample show a significant correlation of IMF slope and surface mass density. The bottom-heavy population (i.e. an excess of low-mass stars in the IMF) is confined to central galaxy regions with surface mass density above $\rm \sim 10^{10}\, M_\odot \, kpc^{-2}$, or, alternatively, within a characteristic radius of ∼2 kpc. Radial distance, in physical units, and surface mass density are the best correlators to IMF variations, with respect to other dynamical (e.g. velocity dispersion) and stellar population (e.g. metallicity) properties. Our results for the most massive galaxies suggest that there is no single parameter that fully explains variations in the stellar IMF, but IMF radial profiles at z ∼ 0 rather result from the complex formation and mass accretion history of galaxy inner and outer regions.
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