58 research outputs found
The definition of environment and its relation to the quenching of galaxies at z=1-2 in a hierarchical Universe
A well calibrated method to describe the environment of galaxies at all
redshifts is essential for the study of structure formation. Such a calibration
should include well understood correlations with halo mass, and the possibility
to identify galaxies which dominate their potential well (centrals), and their
satellites. Focusing on z = 1 and 2 we propose a method of environmental
calibration which can be applied to the next generation of low to medium
resolution spectroscopic surveys. Using an up-to-date semi-analytic model of
galaxy formation, we measure the local density of galaxies in fixed apertures
on different scales. There is a clear correlation of density with halo mass for
satellite galaxies, while a significant population of low mass centrals is
found at high densities in the neighbourhood of massive haloes. In this case
the density simply traces the mass of the most massive halo within the
aperture. To identify central and satellite galaxies, we apply an
observationally motivated stellar mass rank method which is both highly pure
and complete, especially in the more massive haloes where such a division is
most meaningful. Finally we examine a test case for the recovery of
environmental trends: the passive fraction of galaxies and its dependence on
stellar and halo mass for centrals and satellites. With careful calibration,
observationally defined quantities do a good job of recovering known trends in
the model. This result stands even with reduced redshift accuracy, provided the
sample is deep enough to preserve a wide dynamic range of density.Comment: 19 pages, 12 figures, accepted for publication in MNRA
SN Ia host galaxy properties from Sloan Digital Sky Survey-II spectroscopy
We study the stellar populations of Type Ia supernova (SN Ia) host galaxies using Sloan
Digital Sky Survey (SDSS)-II spectroscopy. The main focus is on the relationships of SN Ia
properties with stellar velocity dispersion and the stellar population parameters age, metallicity
and element abundance ratios. We concentrate on a sub-sample of 84 SNe Ia from the
SDSS-II Supernova Survey and find that SALT2 stretch factor values show the strongest dependence
on stellar population age. Hence, more luminous SNe Ia appear in younger stellar
progenitor systems. No statistically significant trends in the Hubble residual with any of the
stellar population parameters studied are found. Moreover, the method of photometric stellar
mass derivation affects the Hubble residual–mass relationship. For an extended sample (247
objects), including SNe Ia with SDSS host galaxy photometry only, the Hubble residual–mass
relationship behaves as a sloped step function. In the high-mass regime, probed by our host
spectroscopy sample, this relationship is flat. Below a stellar mass of ∼2 × 1010M , i.e. close
to the evolutionary transition mass of low-redshift galaxies, the trend changes dramatically
such that lower mass galaxies possess lower luminosity SNe Ia after light-curve corrections.
The sloped step function of the Hubble residual–mass relationship should be accounted for
when using stellar mass as a further parameter for minimizing the Hubble residuals.Department of HE and Training approved lis
First results from the VIRIAL survey: the stellar content of -selected quiescent galaxies at from KMOS
We investigate the stellar populations of 25 massive, galaxies
() at using data obtained with
the K-band Multi-Object Spectrograph (KMOS) on the ESO VLT. Targets were
selected to be quiescent based on their broadband colors and redshifts using
data from the 3D-HST grism survey. The mean redshift of our sample is , where KMOS YJ-band data probe age- and metallicity-sensitive
absorption features in the rest-frame optical, including the band, Fe I,
and high-order Balmer lines. Fitting simple stellar population models to a
stack of our KMOS spectra, we derive a mean age of Gyr.
We confirm previous results suggesting a correlation between color and age for
quiescent galaxies, finding mean ages of Gyr and
Gyr for the reddest and bluest galaxies in our sample.
Combining our KMOS measurements with those obtained from previous studies at
we find evidence for a Gyr spread in the formation epoch of
massive galaxies. At the measured stellar ages are consistent with
passive evolution, while at they appear to saturate at
1 Gyr, which likely reflects changing demographics of the (mean)
progenitor population. By comparing to star-formation histories inferred for
"normal" star-forming galaxies, we show that the timescales required to form
massive galaxies at are consistent with the enhanced
-element abundances found in massive local early-type galaxies.Comment: 6 pages, 5 figures, accepted for publication in ApJ
Growing up in a megalopolis : environmental effects on galaxy evolution in a supercluster at z similar to 0.65 in UKIDSS UDS
We present a large-scale galaxy structure C1 J021734-0513 at z similar to 0.65 discovered in the UKIDSS UDS field, made of similar to 20 galaxy groups and clusters, spreading over 10 Mpc. We report on a VLT/VIMOS spectroscopic follow-up program that, combined with past spectroscopy, allowed us to confirm four galaxy clusters (M-200 similar to 10(14) M-circle dot) and a dozen associated groups and star-forming galaxy overdensities. Two additional filamentary structures at z similar to 0.62 and 0.69 and foreground and background clusters at 0.6 <z <0.7 were also confirmed along the line of sight. The structure subcomponents are at different formation stages. The clusters have a core dominated by passive galaxies and an established red sequence. The remaining structures are a mix of star-forming galaxy overdensities and forming groups. The presence of quiescent galaxies in the core of the latter shows that 'pre-processing' has already happened before the groups fall into their more massive neighbours. Our spectroscopy allows us to derive spectral index measurements e.g. emission/absorption line equivalent widths, strength of the 4000 angstrom break, valuable to investigate the star formation history of structure members. Based on these line measurements, we select a population of 'post-starburst' galaxies. These galaxies are preferentially found within the virial radius of clusters, supporting a scenario in which their recent quenching could be prompted by gas stripping by the dense intracluster medium. We derive stellar age estimates using Markov Chain Monte Carlo-based spectral fitting for quiescent galaxies and find a correlation between ages and colours/stellar masses which favours a top-down formation scenario of the red sequence. A catalogue of similar to 650 redshifts in UDS is released alongside the paper (via MNRAS online data).Peer reviewe
The KMOS3D Survey: Rotating Compact Star-forming Galaxies and the Decomposition of Integrated Line Widths
Using integral field spectroscopy, we investigate the kinematic properties of 35 massive centrally dense and compact star-forming galaxies (SFGs; logM[Ṁ] = 11.1, log (σ 1kpc[Ṁ kpc-2]) > 9.5 log (M∗/re1.5 (Ṁ kpc1.5])> 10.3) at z ∼ 0.7-3.7within the KMOS3D survey. We spatially resolve 23 compact SFGs and find that the majority are dominated by rotational motions with velocities ranging from 95 to 500 km s-1. The range of rotation velocities is reflected in a similar range of integrated 1DUMMYα line widths, 75400 km s-1, consistent with the kinematic properties of mass-matched extended galaxies from the full KMOS3D sample. The fraction of compact SFGs that are classified as rotation-dominated" or "disklike" also mirrors the fractions of the full KMOS3D sample. We show that integrated lineof-sight gas velocity dispersions from KMOS3Dare best approximated by a linear combination of their rotation and turbulent velocities with a lesser but still significant contribution from galactic-scale winds. The 1DUMMYα exponential disk sizes of compact SFGs are, on average, 2.5 ± 0.2 kpc, 1-2 × the continuum sizes, in agreement with previous work. The compact SFGs have a 1.4 × higher active galactic nucleus (AGN) incidence than the full KMOS3D sample at fixed stellar mass with an average AGN fraction of 76%. Given their high and centrally concentrated stellar masses, as well as stellar-to-dynamical mass ratios close to unity, the compact SFGs are likely to have low molecular gas fractions and to quench on a short timescale unless replenished with inflowing gas. The rotation in these compact systems suggests that their direct descendants are rotating passive galaxies.DJW and MF acknowledge
the support of the Deutsche Forschungsgemeinschaft via
Project IDs 3871/1-1 and 3871/1-2. EW acknowledges the
support of ASTRO 3D funding for the writing retreat used to
bring this paper to completion. Parts of this research were
conducted by the Australian Research Council Centre of
Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO
3D) through project number CE170100013
The Kinematics of Massive Quiescent Galaxies at 1.4 < z <2.1: Dark Matter Fractions, IMF Variation, and the Relation to Local Early-type Galaxies
We study the dynamical properties of massive quiescent galaxies at 1.4 DM[e]. Comparing our high-redshift sample to their likely descendants at low redshift, we find that f DM[e] has increased by a factor of more than 4 since z ≈ 1.8, from f DM[e] = 6.6% ± 1.0% to ~24%. The observed increase appears robust to changes in the methods used to estimate dynamical masses or match progenitors and descendants. We quantify possible variation of the stellar IMF through the offset parameter α, defined as the ratio of dynamical mass in stars to the stellar mass estimated using a Chabrier IMF. We demonstrate that the correlation between stellar velocity dispersion and α reported among quiescent galaxies at low redshift is already in place at z = 2, and we argue that subsequent evolution through (mostly minor) merging should act to preserve this relation while contributing significantly to galaxies' overall growth in size and stellar mass
The KMOS Cluster Survey (KCS). I. The Fundamental Plane and the Formation Ages of Cluster Galaxies at Redshift 1.4 < Z < 1.6
We present the analysis of the fundamental plane (FP) for a sample of 19 massive red-sequence galaxies ( ) in three known overdensities at from the K-band Multi-object Spectrograph (KMOS) Cluster Survey, a guaranteed-time program with spectroscopy from the KMOS at the VLT and imaging from the Hubble Space Telescope. As expected, we find that the FP zero-point in B band evolves with redshift, from the value 0.443 of Coma to −0.10 ± 0.09, −0.19 ± 0.05, and −0.29 ± 0.12 for our clusters at z = 1.39, z = 1.46, and z = 1.61, respectively. For the most massive galaxies () in our sample, we translate the FP zero-point evolution into a mass-to-light-ratio M/L evolution, finding , , to , respectively. We assess the potential contribution of the galaxy structural and stellar velocity dispersion evolution to the evolution of the FP zero-point and find it to be ~6%–35% of the FP zero-point evolution. The rate of M/L evolution is consistent with galaxies evolving passively. Using single stellar population models, we find an average age of Gyr for the galaxies in our massive and virialized cluster at z = 1.39, Gyr in a massive but not virialized cluster at z = 1.46, and Gyr in a protocluster at z = 1.61. After accounting for the difference in the age of the universe between redshifts, the ages of the galaxies in the three overdensities are consistent within the errors, with possibly a weak suggestion that galaxies in the most evolved structure are older
The Morphology of Galaxies in the Baryon Oscillation Spectroscopic Survey
We study the morphology of luminous and massive galaxies at 0.3<z<0.7
targeted in the Baryon Oscillation Spectroscopic Survey (BOSS) using publicly
available Hubble Space Telescope imaging from COSMOS. Our sample (240 objects)
provides a unique opportunity to check the visual morphology of these galaxies
which were targeted based solely on stellar population modelling. We find that
the majority (74+/-6%) possess an early-type morphology (elliptical or S0),
while the remainder have a late-type morphology. This is as expected from the
goals of the BOSS target selection which aimed to predominantly select slowly
evolving galaxies, for use as cosmological probes, while still obtaining a fair
fraction of actively star forming galaxies for galaxy evolution studies. We
show that a colour cut of (g-i)>2.35 selects a sub-sample of BOSS galaxies with
90% early-type morphology - more comparable to the earlier Luminous Red Galaxy
(LRG) samples of SDSS-I/II. The remaining 10% of galaxies above this cut have a
late-type morphology and may be analogous to the "passive spirals" found at
lower redshift. We find that 23+/-4% of the early-type galaxies are unresolved
multiple systems in the SDSS imaging. We estimate that at least 50% of these
are real associations (not projection effects) and may represent a significant
"dry merger" fraction. We study the SDSS pipeline sizes of BOSS galaxies which
we find to be systematically larger (by 40%) than those measured from HST
images, and provide a statistical correction for the difference. These details
of the BOSS galaxies will help users of the data fine-tune their selection
criteria, dependent on their science applications. For example, the main goal
of BOSS is to measure the cosmic distance scale and expansion rate of the
Universe to percent-level precision - a point where systematic effects due to
the details of target selection may become important.Comment: 18 pages, 11 figures; v2 as accepted by MNRA
The Kinematics of Massive Quiescent Galaxies at 1.4 < z < 2.1: Dark Matter Fractions, IMF Variation, and the Relation to Local Early-type Galaxies
We study the dynamical properties of massive quiescent galaxies at 1.4 <z <2.1 using deep Hubble Space Telescope WFC3/F160W imaging and a combination of literature stellar velocity dispersion measurements and new near-infrared spectra obtained using the K-band Multi Object Spectrograph(KMOS) on the ESO Very Large Telescope. We use these data to show that the typical dynamical-to-stellar mass ratio has increased by∼0.2 dex from z = 2 to the present day, and we investigate this evolution in the context of possible changes in the stellar initial mass function(IMF) and/or fraction of dark matter contained within the galaxy effective radius,fDM[<re]. Comparing our high-redshift sample to their likely descendants at low redshift, we find that fDM[<re] has increased by a factor of more than 4 since z ≈ 1.8, from fDM[<re] = 6.6% +-1.0% to∼24%. The observed increase appears robust to changes in the methods used to estimate dynamical masses or match progenitors and descendants. We quantify possible variation of the stellar IMF through the offset parameter α, defined as the ratio of dynamical mass in stars to the stellar mass estimated using a Chabrier IMF. We demonstrate that the correlation between stellar velocity dispersion and α reported among quiescent galaxies at low redshift is already in place atz = 2, and we argue that subsequent evolution through (mostly minor) merging should act to preserve this relation while contributing significantly to galaxies'overall growth in size and stellar mass.J.T.M. acknowledges the support of the Australian Research Council Centre of
Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO
3D), through project No. CE170100013. D.J.W. and M.F.
acknowledge the support of the Deutsche Forschungsgemeinschaft via Project IDs 3871/1-1 and 3871/1-2. M.F. has
received funding from the European Research Council (ERC)
under the European Union’s Horizon 2020 research and
innovation program (grant agreement No. 757535)
Sizes, colour gradients and resolved stellar mass distributions for the massive cluster galaxies in XMMUJ2235-2557 at z
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