scholarly journals Dynamical masses of early-type galaxies at z ~ 2

2012 ◽  
Vol 8 (S295) ◽  
pp. 37-44
Author(s):  
Michele Cappellari
Keyword(s):  
Galaxy Formation ◽  
Velocity Dispersion ◽  
High Redshift ◽  
Early Type ◽  
Imaging Data ◽  
Galaxy Dynamics ◽  
Stellar Velocity ◽  
Multi Band ◽  
The Imf

AbstractThe evolution of masses and sizes of passive (early-type) galaxies with redshift provides ideal constraints to galaxy formation models. These parameters can in principle be obtained for large galaxy samples from multi-band photometry alone. However the accuracy of photometric masses is limited by the non-universality of the IMF. Galaxy sizes can be biased at high redshift due to the inferior quality of the imaging data. Both problems can be avoided using galaxy dynamics, and in particular by measuring the galaxies stellar velocity dispersion. Here we provide an overview of the efforts in this direction.

scholarly journals What does (not) drive the variation of the low-mass end of the stellar initial mass function of early-type galaxies

2021 ◽  
Vol 645 ◽  
pp. L1
Author(s):  
C. E. Barbosa ◽  
C. Spiniello ◽  
M. Arnaboldi ◽  
L. Coccato ◽  
M. Hilker ◽  
...  
Keyword(s):  
Stellar Population ◽  
Velocity Dispersion ◽  
Mass Function ◽  
Initial Mass Function ◽  
Population Parameters ◽  
Early Type ◽  
Stellar Velocity ◽  
Stellar Initial Mass Function ◽  
Low Mass ◽  
The Imf

Context. The stellar initial mass function (IMF) seems to be variable and not universal, contrary to what has been argued in the literature over the last three decades. Several relations of the low-mass end of the IMF slope with other stellar population, photometrical, and kinematical parameters of massive early-type galaxies (ETGs) have been proposed, but consensus on the factual cause of the observed variations has not yet been reached. Aims. We investigate the relationship between the IMF and other stellar population parameters in NGC 3311, the central galaxy of the Hydra I cluster. NGC 3311 is a unique laboratory, characterized by old and metal-rich stars, that is similar to other massive ETGs for which the IMF slope has been measured to be bottom-heavy (i.e., dwarf-rich); however, it has unusual stellar velocity dispersion and [α/Fe] profiles, both of which increase with radius. Methods. We use the spatially resolved stellar population parameters (age, total metallicity, and [α/Fe]) that were derived in a forthcoming paper (Barbosa et al. 2020) – via the full-spectrum fitting of high signal-to-noise MUSE observations – to compare the IMF slope in the central part of NGC 3311 (R ≲ 16 kpc) against other stellar parameters, with the goal of assessing their relations and dependencies. Results. For NGC 3311, we unambiguously invalidate the previously observed direct correlation between the IMF slope and the local stellar velocity dispersion, confirming some doubts that had been raised in the literature. This relation may simply arise as a spatial coincidence between the region with the largest stellar velocity dispersion and the region where the oldest in situ population is found and dominates the light. We also show robust evidence that the proposed IMF−metallicity relation is contaminated by the degeneracy between these two parameters. We do confirm that the stellar content in the innermost region of NGC 3311 follows a bottom-heavy IMF, in line with other literature results. The tightest correlations we found are those between stellar age and the IMF and between the galactocentric radius and the IMF. Conclusions. The variation of the IMF at its low-mass end is not due to kinematical, dynamical, or global properties in NGC 3311. We speculate instead that the IMF might be dwarf-dominated in the “red nuggets” that formed through a very short and intense star formation episode at high redshifts (z >  2) when the Universe was denser and richer in gas, and which then ended up being the central cores of today’s giant ellipticals.

scholarly journals IMF radial gradients in most massive early-type galaxies

2019 ◽  
Vol 489 (3) ◽  
pp. 4090-4110 ◽  
Author(s):  
F La Barbera ◽  
A Vazdekis ◽  
I Ferreras ◽  
A Pasquali ◽  
C Allende Prieto ◽  
...  
Keyword(s):  
Stellar Population ◽  
Velocity Dispersion ◽  
Mass Density ◽  
Initial Mass Function ◽  
Early Type ◽  
Low Mass Stars ◽  
Surface Mass ◽  
Low Mass ◽  
Surface Mass Density ◽  
The Imf

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.

scholarly journals Stellar velocity dispersion and initial mass function gradients in dissipationless galaxy mergers

2020 ◽  
Vol 499 (1) ◽  
pp. 559-572
Author(s):  
Carlo Nipoti ◽  
Carlo Cannarozzo ◽  
Francesco Calura ◽  
Alessandro Sonnenfeld ◽  
Tommaso Treu
Keyword(s):  
Velocity Dispersion ◽  
Mass Function ◽  
Initial Mass Function ◽  
Initial Mass ◽  
Galaxy Mergers ◽  
Orbital Parameters ◽  
Spatially Resolved ◽  
Stellar Velocity ◽  
Stellar Initial Mass Function ◽  
The Imf

ABSTRACT The stellar initial mass function (IMF) is believed to be non-universal among early-type galaxies (ETGs). Parametrizing the IMF with the so-called IMF mismatch parameter αIMF, which is a measure of the stellar mass-to-light ratio of an ensemble of stars and thus of the ‘heaviness’ of its IMF, one finds that for ETGs αe (i.e. αIMF integrated within the effective radius Re) increases with σe (the line-of-sight velocity dispersion σlos integrated within Re) and that, within the same ETG, αIMF tends to decrease outwards. We study the effect of dissipationless (dry) mergers on the distribution of the IMF mismatch parameter αIMF in ETGs using the results of binary major and minor merging simulations. We find that dry mergers tend to make the αIMF profiles of ETGs shallower, but do not alter significantly the shape of the distributions in the spatially resolved σlos–αIMF space. Individual galaxies undergoing dry mergers tend to decrease their αe, due to erosion of αIMF gradients and mixing with stellar populations with lighter IMF. Their σe can either decrease or increase, depending on the merging orbital parameters and mass ratio, but tends to decrease for cosmologically motivated merging histories. The αe–σe relation can vary with redshift as a consequence of the evolution of individual ETGs: based on a simple dry-merging model, ETGs of given σe are expected to have higher αe at higher redshift, unless the accreted satellites are so diffuse that they contribute negligibly to the inner stellar distribution of the merger remnant.

scholarly journals Elliptical Galaxies: Darkly Cloaked or Scantily Clad?

2004 ◽  
Vol 220 ◽  
pp. 165-170
Author(s):  
A. J. Romanowsky ◽  
N. G. Douglas ◽  
K. Kuijken ◽  
M. R. Merrifield ◽  
M. Arnaboldi ◽  
...  
Keyword(s):  
Galaxy Formation ◽  
Velocity Dispersion ◽  
Elliptical Galaxies ◽  
Small Sample ◽  
Early Type ◽  
Dynamical Models ◽  
Show Evidence ◽  
Major Merger ◽  
Nearby Galaxies ◽  
Ab Initio Models

Planetary nebulae (PNe) may be the most promising tracers in the halos of early-type galaxies. We have used multi-object spectrographs on the WHT and the VLT, and the new Planetary Nebula Spectrograph on the WHT, to obtain hundreds of PN velocities in a small sample of nearby galaxies. These ellipticals show weak halo rotation, which may be consistent with ab initio models of galaxy formation, but not with more detailed major merger simulations. the galaxies near L* show evidence of a universal declining velocity dispersion profile, and dynamical models indicate the presence of little dark matter within 5 Reff—implying halos either not as massive or not as centrally concentrated as CDM predicts.

scholarly journals Galaxy formation and evolution using multi-wavelength, multi-resolution imaging data in the Virtual Observatory

2006 ◽  
Vol 2 (14) ◽  
pp. 592-592
Author(s):  
Paresh Prema ◽  
Nicholas A. Walton ◽  
Richard G. McMahon
Keyword(s):  
Galaxy Formation ◽  
High Redshift ◽  
Large Data ◽  
Electromagnetic Spectrum ◽  
Data Sets ◽  
Virtual Observatory ◽  
X Rays ◽  
Imaging Data ◽  
Wide Range ◽  
Multi Wavelength

Observational astronomy is entering an exciting new era with large surveys delivering deep multi-wavelength data over a wide range of the electromagnetic spectrum. The last ten years has seen a growth in the study of high redshift galaxies discovered with the method pioneered by Steidel et al. (1995) used to identify galaxies above z>1. The technique is designed to take advantage of the multi-wavelength data now available for astronomers that can extend from X-rays to radio wavelength. The technique is fast becoming a useful way to study large samples of objects at these high redshifts and we are currently designing and implementing an automated technique to study these samples of objects. However, large surveys produce large data sets that have now reached terabytes (e.g. for the Sloan Digital Sky Survey, <http://www.sdss.org>) in size and petabytes over the next 10yr (e.g., LSST, <http://www.lsst.org>). The Virtual Observatory is now providing a means to deal with this issue and users are now able to access many data sets in a quicker more useful form.

scholarly journals Ages and metallicities of early-type galaxies

2009 ◽  
Vol 5 (S262) ◽  
pp. 400-401
Author(s):  
Ricardo Ogando ◽  
Marcio Maia ◽  
Paulo Pellegrini ◽  
Luiz da Costa
Keyword(s):  
Star Formation ◽  
Hierarchical Clustering ◽  
Galaxy Formation ◽  
Velocity Dispersion ◽  
Stellar Populations ◽  
Theoretical Framework ◽  
High Density ◽  
Early Type ◽  
Massive Galaxies ◽  
Low Mass

AbstractThe study of stellar populations in early-type galaxies give us clues on how they form and evolve. We calculate age, [Z/H], and [α/Fe] ratio for 162 early-type galaxies using the SSP models from Thomas, Maraston, & Bender (2003) applied to Lick indices measurements, such as Hβ, Mgb, Fe5270 and Fe5335. Those were obtained from longslit spectra observed in the ESO 1.52m telescope as described in Ogando et al. (2008). We study the relations between the SSP parameters and velocity dispersion, as well as the influence of environment on these relations. We find that age, [Z/H], and [α/Fe] correlate well with velocity dispersion, so that more massive galaxies, have on average, higher metallicities, ages and abundance ratios than that of the low-mass ones. Galaxies in high density regions are older and more metal-rich than those in regions with low number of neighbors. These results are not consistent with standard predictions of hierarchical clustering. In the last decade, this “anti-hierarchical” behavior has also been generally tagged as downsizing and has challenged the current theoretical framework of galaxy formation, calling for new ways of star formation regulation in early-type galaxies.

scholarly journals Discovery of an unusually compact lensed Lyman-break galaxy from the Hyper Suprime-Cam Survey

2020 ◽  
Vol 494 (3) ◽  
pp. 3156-3165 ◽  
Author(s):  
Anton T Jaelani ◽  
Anupreeta More ◽  
Alessandro Sonnenfeld ◽  
Masamune Oguri ◽  
Cristian E Rusu ◽  
...  
Keyword(s):  
Velocity Dispersion ◽  
High Redshift ◽  
Mass Model ◽  
Sharp Drop ◽  
Stellar Velocity ◽  
Absorption Features ◽  
Early Type Galaxy ◽  
Einstein Radius ◽  
Good Agreement

ABSTRACT We report the serendipitous discovery of HSC J0904–0102, a quadruply lensed Lyman-break galaxy (LBG) in the Survey of Gravitationally-lensed Objects in Hyper Suprime-Cam Imaging (SuGOHI). Owing to its point-like appearance, the source was thought to be a lensed active galactic nucleus. We obtained follow-up spectroscopic data with the Gemini Multi-Object Spectrographs on the Gemini South Telescope, which confirmed this to be a lens system. The deflecting foreground galaxy is a typical early-type galaxy at a high redshift of $z_{\ell}=0.957$ with stellar velocity dispersion $\sigma_v=259\pm56$ km s−1. The lensed source is identified as an LBG at $z_{\rm s}=3.403$, based on the sharp drop bluewards of Lyα and other absorption features. A simple lens mass model for the system, assuming a singular isothermal ellipsoid, yields an Einstein radius of $\theta_{\rm Ein}=1.23$ arcsec and a total mass within the Einstein radius of $M_{\rm Ein}=(5.55\pm0.24)\times10^{11}\rm M_{\odot}$ corresponding to a velocity dispersion of $\sigma_{\rm SIE}=283\pm3$ km s−1, which is in good agreement with the value derived spectroscopically. The most isolated lensed LBG image has a magnification of $\sim 6.5$. In comparison with other lensed LBGs and typical $z\sim4$ LBG populations, HSC J0904–0102 is unusually compact, an outlier at $&gt;2\sigma$ confidence. Together with a previously discovered SuGOHI lens, HSC J1152+0047, which is similarly compact, we believe that the HSC survey is extending LBG studies down to smaller galaxy sizes.

scholarly journals Scaling relations in early-type galaxies from integral-field stellar kinematics

2009 ◽  
Vol 5 (H15) ◽  
pp. 81-81
Author(s):  
M. Cappellari ◽  
N. Scott ◽  
K. Alatalo ◽  
L. Blitz ◽  
M. Bois ◽  
...  
Keyword(s):  
Surface Brightness ◽  
Velocity Dispersion ◽  
Scaling Relations ◽  
Early Type ◽  
Stellar Kinematics ◽  
Fundamental Plane ◽  
The Past ◽  
Stellar Velocity ◽  
Integral Field ◽  
Significant Effort

Early-type galaxies (ETGs) satisfy a now classic scaling relation Re ∝ σ1.2eI−0.8e, the Fundamental Plane (FP; Djorgovski & Davis 1987; Dressler et al. 1987), between their size, stellar velocity dispersion and mean surface brightness. A significant effort has been devoted in the past twenty years to try to understand why the coefficients of the relation are not the ones predicted by the virial theorem Re ∝ σ2eI−1e.

Evidence for Initial Mass Function Variation in Massive Early-Type Galaxies

2020 ◽  
Vol 58 (1) ◽  
pp. 577-615 ◽  
Author(s):  
Russell J. Smith
Keyword(s):  
Gravitational Lensing ◽  
High Redshift ◽  
Mass Function ◽  
Spectroscopic Studies ◽  
Initial Mass Function ◽  
Initial Mass ◽  
Early Type ◽  
Stellar Component ◽  
The Imf

The initial mass function (IMF), describing the distribution of birth masses of stars, plays a pivotal role in establishing the observable properties of galaxies. This article reviews the evidence for variation in the IMF of massive early-type galaxies (ETGs), especially from spectroscopic studies and from dynamical and gravitational lensing measurements over the past decade. The principal conclusions are as follows: ▪  The spectra of massive ETGs depart from the predictions of models with Milky Way–like IMFs in a way that is best reproduced by assuming a steeper (bottom-heavy) IMF below ∼1 M⊙. ▪  Lensing and dynamical models, assuming a constant mass-to-light ratio for the stellar component, infer heavy IMFs, superficially supporting the result from spectra. ▪  The spectroscopic signal exhibits a steep gradient, however, and may be confined to the innermost region with scales ≲2 kpc; such internal variation in the stellar mass-to-light ratio would invalidate a key assumption of most dynamics and lensing studies. ▪  For masses above the main sequence turnoff in ancient populations (≳1 M⊙), there is little evidence for a steeper IMF in massive ETGs or their high-redshift progenitors; rather, a slightly shallower slope is preferred in this regime from several different arguments. ▪  Steep internal gradients may be responsible for some of the apparent discrepancies between different methods and also point to the cause of the IMF variation being restricted to conditions specific to the in situ formation phase of ETG cores.

scholarly journals The cosmic evolution of the stellar mass–velocity dispersion relation of early-type galaxies

2020 ◽  
Vol 498 (1) ◽  
pp. 1101-1120
Author(s):  
Carlo Cannarozzo ◽  
Alessandro Sonnenfeld ◽  
Carlo Nipoti
Keyword(s):  
Mass Velocity ◽  
Selection Criteria ◽  
Velocity Dispersion ◽  
State Of The Art ◽  
Stellar Mass ◽  
Early Type ◽  
Bayesian Hierarchical ◽  
Cosmic Evolution ◽  
Stellar Velocity ◽  
Intrinsic Scatter

ABSTRACT We study the evolution of the observed correlation between central stellar velocity dispersion σe and stellar mass M* of massive ($M_*\gtrsim 3\times 10^{10}\, \mathrm{M_\odot}$) early-type galaxies (ETGs) out to redshift z ≈ 2.5, taking advantage of a Bayesian hierarchical inference formalism. Collecting ETGs from state-of-the-art literature samples, we build a fiducial sample (0 ≲ z ≲ 1), which is obtained with homogeneous selection criteria, but also a less homogeneous extended sample (0 ≲ z ≲ 2.5). Based on the fiducial sample, we find that at z ≲ 1 the M*–σe relation is well represented by $\sigma _{\mathrm{e}}\propto M_*^{\beta }(1+z)^{\zeta}$, with β ≃ 0.18 independent of redshift and ζ ≃ 0.4 (at a given M*, σe decreases for decreasing z, for instance by a factor of ≈1.3 from z = 1 to z = 0). When the slope β is allowed to evolve, we find it increasing with redshift: β(z) ≃ 0.16 + 0.26log (1 + z) describes the data as well as constant β ≃ 0.18. The intrinsic scatter of the M*–σe relation is ≃0.08 dex in σe at given M*, independent of redshift. Our results suggest that, on average, the velocity dispersion of individual massive (M* ≳ 3 × 1011M⊙) ETGs decreases with time while they evolve from z ≈ 1 to z ≈ 0. The analysis of the extended sample, over the wider redshift range 0 ≲ z ≲ 2.5, leads to results similar to that of the fiducial sample, with slightly stronger redshift dependence of the normalization (ζ ≃ 0.5) and weaker redshift dependence of the slope (dβ/dlog (1 + z) ≃ 0.18) when β varies with time. At z = 2 ETGs with $M_*\approx 10^{11}\, \mathrm{M_\odot}$ have, on average, ≈1.7 higher σe than ETGs of similar stellar mass at z = 0.

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