arXiv subjects

Jesse van de Sande

Publications and source records attributed to Jesse van de Sande.

104 records · Page 6Linked to original sources

arXiv2017

The SAMI Galaxy Survey: mass as the driver of the kinematic morphology - density relation in clusters

We examine the kinematic morphology of early-type galaxies (ETGs) in eight galaxy clusters in the Sydney-AAO Multi-object Integral field spectrograph (SAMI) Galaxy Survey. The clusters cover a mass range of 14.2<log(M_200/M_odot)<15.2 and we measure spatially-resolved stellar kinematics for 315 member galaxies with stellar masses 10.0<log(M_*/M_odot)<11.7 within 1R_200 of the cluster centers. We calculate the spin parameter, lambda_R and use that to classify the kinematic morphology of the galaxies as fast or slow rotators. The total fraction of slow rotators in the early-type galaxy population, F_SR=0.14+/-0.02 and does not depend on host cluster mass. Across the eight clusters, the fraction of slow rotators increases with increasing local overdensity. We also find that the slow-rotator fraction increases at small clustercentric radii (R_cl<0.3R_200), and note that there is also an increase in slow-rotator fraction at R_cl~0.6R_200. The slow rotators at these larger radii reside in cluster substructure. We find the strongest increase in slow-rotator fraction occurs with increasing stellar mass. After accounting for the strong correlation with stellar mass, we find no significant relationship between spin parameter and local overdensity in the cluster environment. We conclude that the primary driver for the kinematic morphology--density relationship in galaxy clusters is the changing distribution of galaxy stellar mass with local environment. The presence of slow rotators in substructure suggests that the cluster kinematic morphology--density relationship is a result of mass segregation of slow-rotating galaxies forming in groups that later merge with clusters and sink to the cluster center via dynamical friction.

astro-ph.GA↗

arXiv2016

The SAMI Galaxy Survey: Revisiting Galaxy Classification Through High-Order Stellar Kinematics

Recent cosmological hydrodynamical simulations suggest that integral field spectroscopy can connect the high-order stellar kinematic moments h3 (~skewness) and h4 (~kurtosis) in galaxies to their cosmological assembly history. Here, we assess these results by measuring the stellar kinematics on a sample of 315 galaxies, without a morphological selection, using 2D integral field data from the SAMI Galaxy Survey. A proxy for the spin parameter ($λ_{R_e}$) and ellipticity ($ε_e$) are used to separate fast and slow rotators; there exists a good correspondence to regular and non-regular rotators, respectively, as also seen in earlier studies. We confirm that regular rotators show a strong h3 versus $V/σ$ anti-correlation, whereas quasi-regular and non-regular rotators show a more vertical relation in h3 and $V/σ$. Motivated by recent cosmological simulations, we develop an alternative approach to kinematically classify galaxies from their individual h3 versus $V/σ$ signatures. We identify five classes of high-order stellar kinematic signatures using Gaussian mixture models. Class 1 corresponds to slow rotators, whereas Classes 2-5 correspond to fast rotators. We find that galaxies with similar $λ_{R_e}-ε_e$ values can show distinctly different h3-$V/σ$ signatures. Class 5 objects are previously unidentified fast rotators that show a weak h3 versus $V/σ$ anti-correlation. These objects are predicted to be disk-less galaxies formed by gas-poor mergers. From morphological examination, however, there is evidence for large stellar disks. Instead, Class 5 objects are more likely disturbed galaxies, have counter-rotating bulges, or bars in edge-on galaxies. Finally, we interpret the strong anti-correlation in h3 versus $V/σ$ as evidence for disks in most fast rotators, suggesting a dearth of gas-poor mergers among fast rotators.

astro-ph.GA↗

arXiv2016

The SAMI galaxy survey: Galaxy Interactions and Kinematic Anomalies in Abell 119

Galaxy mergers are important events that can determine the fate of a galaxy by changing its morphology, star-formation activity and mass growth. Merger systems have commonly been identified from their disturbed morphologies, and we now can employ Integral Field Spectroscopy to detect and analyze the impact of mergers on stellar kinematics as well. We visually classified galaxy morphology using deep images ($μ_{\rm r} = 28\,\rm mag\,\, arcsec^{-2}$) taken by the Blanco 4-m telescope at the Cerro Tololo Inter-American Observatory. In this paper we investigate 63 bright ($M_{\rm r}<-19.3$) spectroscopically-selected galaxies in Abell 119; of which 53 are early type and 20 galaxies show a disturbed morphology by visual inspection. A misalignment between the major axes in the photometric image and the kinematic map is conspicuous in morphologically-disturbed galaxies. Our sample is dominated by early-type galaxies, yet it shows a surprisingly tight Tully-Fisher relation except for the morphologically-disturbed galaxies which show large deviations. Three out of the eight slow rotators in our sample are morphology disturbed. The visually-selected morphologically-disturbed galaxies are generally more asymmetric, visually as well as kinematically. Our findings suggest that galaxy interactions, including mergers and perhaps fly-bys, play an important role in determining the orientation and magnitude of galaxy's angular momentum.

astro-ph.GA↗

arXiv2016

Hector - a new massively multiplexed IFS instrument for the Anglo-Australian Telescope

Hector will be the new massively-multiplexed integral field spectroscopy (IFS) instrument for the Anglo-Australian Telescope (AAT) in Australia and the next main dark-time instrument for the observatory. Based on the success of the SAMI instrument, which is undertaking a 3400-galaxy survey, the integral field unit (IFU) imaging fibre bundle (hexabundle) technology under-pinning SAMI is being improved to a new innovative design for Hector. The distribution of hexabundle angular sizes is matched to the galaxy survey properties in order to image 90% of galaxies out to 2 effective radii. 50-100 of these IFU imaging bundles will be positioned by 'starbug' robots across a new 3-degree field corrector top end to be purpose-built for the AAT. Many thousand fibres will then be fed into new replicable spectrographs. Fundamentally new science will be achieved compared to existing instruments due to Hector's wider field of view (3 degrees), high positioning efficiency using starbugs, higher spectroscopic resolution (R~3000-5500 from 3727-7761A, with a possible redder extension later) and large IFUs (up to 30 arcsec diameter with 61-217 fibre cores). A 100,000 galaxy IFS survey with Hector will decrypt how the accretion and merger history and large-scale environment made every galaxy different in its morphology and star formation history. The high resolution, particularly in the blue, will make Hector the only instrument to be able to measure higher-order kinematics for galaxies down to much lower velocity dispersion than in current large IFS galaxy surveys, opening up a wealth of new nearby galaxy science.

astro-ph.IM↗

arXiv2016

The evolution in the stellar mass of Brightest Cluster Galaxies over the past 10 billion years

Using a sample of 98 galaxy clusters recently imaged in the near infra-red with the ESO NTT, WIYN and WHT telescopes, supplemented with 33 clusters from the ESO archive, we measure how the stellar mass of the most massive galaxies in the universe, namely Brightest Cluster Galaxies (BCG), increases with time. Most of the BCGs in this new sample lie in the redshift range $0.2<z<0.6$, which has been noted in recent works to mark an epoch over which the growth in the stellar mass of BCGs stalls. From this sample of 132 clusters, we create a subsample of 102 systems that includes only those clusters that have estimates of the cluster mass. We combine the BCGs in this subsample with BCGs from the literature, and find that the growth in stellar mass of BCGs from 10 billion years ago to the present epoch is broadly consistent with recent semi-analytic and semi-empirical models. As in other recent studies, tentative evidence indicates that the stellar mass growth rate of BCGs may be slowing in the past 3.5 billion years. Further work in collecting larger samples, and in better comparing observations with theory using mock images is required if a more detailed comparison between the models and the data is to be made.

astro-ph.GA↗

arXiv2016

Stellar Velocity Dispersion for a Strongly-Lensed, Intermediate-Mass Quiescent Galaxy at z=2.8

Measuring stellar velocity dispersions of quiescent galaxies beyond $z\sim2$ is observationally challenging. Such measurements require near-infrared spectra with a continuum detection of at least moderate signal-to-noise, often necessitating long integrations. In this paper, we present deep X-Shooter spectroscopy of one of only two known gravitationally-lensed massive quiescent galaxies at $z>2$. This galaxy is quadruply imaged, with the brightest images magnified by a factor of $\sim5$. The total exposure time of our data is 9.8 hours on-source; however the magnification, and the slit placement encompassing 2 images, provides a total equivalent exposure time of 215 hours. From this deep spectrum we measure a redshift ($z_{\mathrm{spec}}=2.756\pm0.001$), making this one of the highest redshift quiescent galaxies that is spectroscopically confirmed. We simultaneously fit both the spectroscopic and photometric data to determine stellar population parameters and conclude this galaxy is relatively young, intermediate-mass, consistent with low dust content, and has quenched only relatively recently. This recent quenching is confirmed by strong Balmer absorption, particularly $Hδ$. Remarkably, this proves that at least some intermediate-mass galaxies have already quenched as early as $z\sim2.8$. Additionally, we have measured a velocity dispersion ($σ=187\pm43~\mathrm{km/s}$), making this the highest-redshift quiescent galaxy with a dispersion measurement. We confirm that this galaxy falls on the same mass fundamental plane (MFP) as galaxies at z=2.2, consistent with little to no evolution in the MFP up to z=2.8. Overall this galaxy is proof of existence of intermediate-mass quenched galaxies in the distant universe, and that lensing is a powerful tool for determining their properties with improved accuracy.

astro-ph.GA↗

arXiv2014

The Relation between Dynamical Mass-to-Light Ratio and Color for Massive Quiescent Galaxies out to z~2 and Comparison with Stellar Population Synthesis Models

We explore the relation between the dynamical mass-to-light ratio ($M/L$) and rest-frame color of massive quiescent galaxies out to z~2. We use a galaxy sample with measured stellar velocity dispersions in combination with Hubble Space Telescope and ground-based multi-band photometry. Our sample spans a large range in $\log M_{dyn}/L_{g}$ (of 1.6~dex) and $\log M_{dyn}/L_{K}$ (of 1.3~dex). There is a strong, approximately linear correlation between the $M/L$ for different wavebands and rest-frame color. The root-mean-scatter scatter in $\log~M_{dyn}/L$ residuals implies that it is possible to estimate the $M/L$ with an accuracy of ~0.25 dex from a single rest-frame optical color. Stellar population synthesis (SPS) models with a Salpeter stellar initial mass function (IMF) can not simultaneously match $M_{dyn}/L_{g}$ vs. $(g-z)_{rest-frame}$ and $M_{dyn}/L_{K}$ vs. $(g-K)_{rest-frame}$. By changing the slope of the IMF we are still unable to explain the M/L of the bluest and reddest galaxies. We find that an IMF with a slope between $α=2.35$ and $α=1.35$ provides the best match. We also explore a broken IMF with a Salpeter slope at $M<1M_{\odot}$ and $M>4M_{\odot}$ and a slope $α$ in the intermediate region. The data favor a slope of $α=1.35$ over $α=2.35$. Nonetheless, our results show that variations between different SPS models are comparable to the IMF variations. In our analysis we assume that the variation in $M/L$ and color is driven by differences in age, and that other contributions (e.g., metallicity evolution, dark matter) are small. These assumptions may be an important source of uncertainty as galaxies evolve in more complex ways.

astro-ph.GA↗

arXiv2014

The Fundamental Plane of massive quiescent galaxies out to z~2

The Fundamental Plane (FP) of early-type galaxies, relating the effective radius, velocity dispersion, and surface brightness, has long been recognized as a unique tool for analyzing galaxy structure and evolution. With the discovery of distant quiescent galaxies and the introduction of high sensitivity near-infrared spectrographs, it is now possible to explore the FP out to z~2. In this Letter we study the evolution of the FP out to z~2 using kinematic measurements of massive quiescent galaxies ($M_{*}>10^{11} M_{\odot}$). We find preliminary evidence for the existence of an FP out to z~2. The scatter of the FP, however, increases from z~0 to z~2, even when taking into account the larger measurement uncertainties at higher redshifts. We find a strong evolution of the zero point from z~2 to z~0: $Δ\log_{10}M/L_g\propto(-0.49\pm0.03)~z$. In order to assess whether our spectroscopic sample is representative of the early-type galaxy population at all redshifts, we compare their rest-frame g-z colors with those from a larger mass complete sample of quiescent galaxies. At z>1 we find that the spectroscopic sample is bluer. We use the color offsets to estimate a mass-to-light ratio (M/L) correction. The implied FP zero point evolution after correction is significantly smaller: $Δ\log_{10}M/L_g\propto(-0.39\pm 0.02)~z$. This is consistent with an apparent formation redshift of $z_{\rm{form}}=6.62^{+3.19}_{-1.44}$ for the underlying population, ignoring the effects of progenitor bias. A more complete spectroscopic sample is required at z~2 to properly measure the M/L evolution from the FP evolution.

astro-ph.GA↗

arXiv2013

Tight Correlations Between Massive Galaxy Structural Properties and Dynamics: The Mass Fundamental Plane Was in Place by z~2

The Fundamental Plane (FP) is an empirical relation between the size, surface brightness, and velocity dispersion of early-type galaxies. This relation has been studied extensively for early-type galaxies in the local universe to constrain galaxy formation mechanisms. The evolution of the zeropoint of this plane has been extended to high redshifts to study the luminosity evolution of massive galaxies, under the assumption of structural homology. In this work, we assess this assumption by replacing surface brightness with stellar mass density and present the evolution of the "mass FP" for massive, quiescent galaxies since z~2. By accounting for stellar populations, we thereby isolate and trace structural and dynamical evolution. Despite the observed dramatic evolution in the sizes and morphologies of massive galaxies since z~3, we find that quiescent galaxies lie on the mass FP out to z~2. In contrast with ~1.4 dex evolution in the luminosity FP, average residuals from the z~0 mass FP are less than ~0.15 dex since z~2. Assuming the Hyde & Bernardi (2009) mass FP slope, we find that this minimal offset scales as (1+z)^{-0.095+/-0.043}. This result lends credence to previous studies that derived luminosity evolution from the FP. Therefore, despite their compact sizes and suggestions that massive galaxies are more disk-like at z~2, the relationship between their dynamics and structural properties are consistent with local early-type galaxies. Finally, we find no strong evidence for a tilt of the mass FP relative to the Virial plane, but emphasize the need for full models including selection biases to fully investigate this issue.

astro-ph.CO↗

arXiv2013

Stellar Kinematics of z~2 Galaxies and the Inside-Out Growth of Quiescent Galaxies

Using stellar kinematics measurements, we investigate the growth of massive, quiescent galaxies from z~2 to today. We present X-Shooter spectra from the UV to NIR and dynamical mass measurements of 5 quiescent massive (>10^11 Msun) galaxies at z~2. This triples the sample of z>1.5 galaxies with well constrained (dsigma <100 km/s) velocity dispersion measurements. From spectral population synthesis modeling we find that these galaxies have stellar ages that range from 0.5-2 Gyr, with no signs of ongoing star formation. We measure velocity dispersions (290-450 km/s) from absorption lines and find that they are 1.6-2.1 times higher than those of galaxies in the SDSS at the same mass. Sizes are measured using GALFIT from HST-WFC3 H160 and UDS K-band images. The dynamical masses correspond well to the SED based stellar masses, with dynamical masses that are ~15% higher. We find that M_*/M_dyn may decrease slightly with time, which could reflect the increase of the dark matter fraction within an increasing effective radius. We combine different stellar kinematic studies from the literature, and examine the structural evolution from z~2 to z~0: we confirm that at fixed dynamical mass, the effective radius increases by a factor of ~2.8, and the velocity dispersion decreases by a factor of ~1.7. The mass density within one effective radius decreases by a factor of ~20, while within a fixed physical radius (1 kpc) it decreases only mildly (~2). When we allow for an evolving mass limit by selecting a population of galaxies at fixed number density, a stronger size growth with time is found (~4), velocity dispersion decreases by a factor of ~1.4, and interestingly, the mass density within 1 kpc is consistent with no evolution. This finding suggests that massive quiescent galaxies at ~2 grow inside-out, consistent with the expectations from minor mergers.

astro-ph.CO↗

arXiv2012

A Strongly-Lensed Massive Ultra-Compact Quiescent Galaxy at z ~ 2.4 in the COSMOS/UltraVISTA Field

We report the discovery of a massive ultra-compact quiescent galaxy that has been strongly-lensed into multiple images by a foreground galaxy at z = 0.960. This system was serendipitously discovered as a set of extremely Ks-bright high-redshift galaxies with red J - Ks colors using new data from the UltraVISTA YJHKs near-infrared survey. The system was also previously identified as an optically-faint lens/source system using the COSMOS ACS imaging by Faure et al. (2008, 2011). Photometric redshifts for the three brightest images of the source galaxy determined from twenty-seven band photometry place the source at z = 2.4 +/- 0.1. We provide an updated lens model for the system which is a good fit to the positions and morphologies of the galaxies in the ACS image. The lens model implies that the magnification of the three brightest images is a factor of 4 - 5. We use the lens model, combined with the Ks-band image to constrain the size and Sersic profile of the galaxy. The best-fit model is an ultra-compact galaxy (Re = 0.64^{+0.08}_{-0.18} kpc, lensing-corrected), with a Sersic profile that is intermediate between a disk and bulge profile (n = 2.2^{+2.3}_{-0.9}). We present aperture photometry for the source galaxy images which have been corrected for flux contamination from the central lens. The best-fit stellar population model is a massive galaxy (Log(M_{star}/M_{sol}) = 10.8^{+0.1}_{-0.1}, lensing-corrected) with an age of 1.0^{+1.0}_{-0.4} Gyr, moderate dust extinction (Av = 0.8^{+0.5}_{-0.6}), and a low specific star formation rate (Log(SSFR) < -11.0 yr^{-1}). This is typical of massive "red-and-dead" galaxies at this redshift and confirms that this source is the first bona fide strongly-lensed massive ultra-compact quiescent galaxy to be discovered. We conclude with a discussion of the prospects of finding a larger sample of these galaxies.

astro-ph.CO↗

arXiv2012

Massive and Newly Dead: Discovery of a Significant Population of Galaxies with High Velocity Dispersions and Strong Balmer Lines at z~1.5 from Deep Keck Spectra and HST/WFC3 Imaging

We present deep Keck/LRIS spectroscopy and HST/WFC3 imaging in the rest-frame optical for a sample of eight galaxies at z~1.5 with high photometrically-determined stellar masses. The data are combined with VLT/XShooter spectra of five galaxies from van de Sande et al. (2011, 2012 to be submitted). We find that these thirteen galaxies have high velocity dispersions, with a median of sigma=301 km s^{-1}. This high value is consistent with their relatively high stellar masses and compact sizes. We study their stellar populations using the strength of Balmer absorption lines, which are not sensitive to dust absorption. We find a large range in Balmer absorption strength, with many galaxies showing very strong lines indicating young ages. The median Hdelta_A equivalent width, determined directly or inferred from the H10 line, is 5.4 Angstroms, indicating a luminosity-weighted age of ~1 Gyr. Although this value may be biased towards higher values because of selection effects,high-dispersion galaxies with such young ages are extremely rare in the local Universe. Interestingly we do not find a simple correlation with rest-frame U-V color: some of the reddest galaxies have very strong Balmer absorption lines. These results demonstrate that many high-dispersion galaxies at z~1.5 were quenched recently. This implies that there must be a population of star-forming progenitors at z~2 with high velocity dispersions or linewidths, which are notoriously absent from CO/Halpha selected surveys.

astro-ph.CO↗

arXiv2011

Redshift Evolution of the Galaxy Velocity Dispersion Function

We present a study of the evolution of the galaxy Velocity Dispersion Function (VDF) from z=0 to z=1.5 using photometric data from the UKIDSS Ultra Deep Survey (UDS) and Newfirm Medium Band Survey (NMBS) COSMOS surveys. The VDF has been measured locally using direct kinematic measurements from the Sloan Digital Sky Survey, but direct studies of the VDF at high redshift are difficult as they require velocity dispersion measurements of many thousands of galaxies. Taylor et al. (2010) demonstrated that dynamical and stellar mass are linearly related when the structure of the galaxy is accounted for. We show that the stellar mass, size and Sérsic index can reliably predict the velocity dispersions of SDSS galaxies. We apply this relation to galaxies at high redshift and determine the evolution of the inferred VDF. We find that the VDF at z~0.5 is very similar to the VDF at z=0. At higher redshifts, we find that the number density of galaxies with dispersions <~200 km/s is lower, but the number of high dispersion galaxies is constant or even higher. At fixed cumulative number density, the velocity dispersions of galaxies with logN[Mpc^{-3}]<-3.5 increase with time by a factor of ~1.4 from z~1.5-0, whereas the dispersions of galaxies with lower number density are approximately constant or decrease with time. The VDF appears to show less evolution than the stellar mass function, particularly at the lowest number densities. We note that these results are still somewhat uncertain and we suggest several avenues for further calibrating the inferred velocity dispersions.

astro-ph.CO↗

arXiv2011

The stellar velocity dispersion of a compact massive galaxy at z=1.80 using X-Shooter: confirmation of the evolution in the mass-size and mass-dispersion relations

Recent photometric studies have shown that early-type galaxies at fixed stellar mass were smaller and denser at earlier times. In this paper we assess that finding by deriving the dynamical mass of such a compact quiescent galaxy at z=1.8. We have obtained a high-quality spectrum with full UV-NIR wavelength coverage of galaxy NMBS-C7447 using X-Shooter on the VLT. We determined a velocity dispersion of 294 +- 51 km/s. Given this velocity dispersion and the effective radius of 1.64 +- 0.15 kpc (as determined from HST-WFC3 F160W observations) we derive a dynamical mass of 1.7 +- 0.5 x 10^11 Msun. Comparison of the full spectrum with stellar population synthesis models indicates that NMBS-C774 has a relatively young stellar population (0.40 Gyr) with little or no star formation and a stellar mass of ~1.5 x 10^11 Msun. The dynamical and photometric stellar mass are in good agreement. Thus, our study supports the conclusion that the mass densities of quiescent galaxies were indeed higher at earlier times, and this earlier result is not caused by systematic measurement errors. By combining available spectroscopic measurements at different redshifts, we find that the velocity dispersion at fixed dynamical mass was a factor of ~1.8 higher at z=1.8 compared to z=0. Finally, we show that the apparent discrepancies between the few available velocity dispersion measurements at z>1.5 are consistent with the intrinsic scatter of the mass-size relation.

astro-ph.CO↗