arXiv subjects

Gabriel Brammer

Publications and source records attributed to Gabriel Brammer.

At least 271 records · Page 15Linked to original sources

arXiv2018

HFF-DeepSpace Photometric Catalogs of the Twelve Hubble Frontier Fields, Clusters and Parallels: Photometry, Photometric Redshifts, and Stellar Masses

We present Hubble multi-wavelength photometric catalogs, including (up to) 17 filters with the Advanced Camera for Surveys and Wide Field Camera 3 from the ultra-violet to near-infrared for the Hubble Frontier Fields and associated parallels. We have constructed homogeneous photometric catalogs for all six clusters and their parallels. To further expand these data catalogs, we have added ultra-deep $K_{S}$-band imaging at 2.2~\micron\ from the Very Large Telescope HAWK-I and Keck-I MOSFIRE instruments. We also add post-cryogenic \spitzer\ imaging at 3.6~\micron\ and 4.5~\micron\ with the Infrared Array Camera (IRAC), as well as archival IRAC 5.8~\micron\ and 8.0~\micron\ imaging when available. We introduce the public release of the multi-wavelength (0.2--8~\micron) photometric catalogs, and we describe the unique steps applied for the construction of these catalogs. Particular emphasis is given to the source detection band, the contamination of light from the bright cluster galaxies and intra-cluster light. In addition to the photometric catalogs, we provide catalogs of photometric redshifts and stellar population properties. Furthermore, this includes all the images used in the construction of the catalogs, including the combined models of bright cluster galaxies and intra-cluster light, the residual images, segmentation maps and more. These catalogs are a robust data set of the Hubble Frontier Fields and will be an important aide in designing future surveys, as well as planning follow-up programs with current and future observatories to answer key questions remaining about first light, reionization, the assembly of galaxies and many more topics, most notably, by identifying high-redshift sources to target.

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arXiv2017

Type Ia Supernova Distances at z > 1.5 from the Hubble Space Telescope Multi-Cycle Treasury Programs: The Early Expansion Rate

We present an analysis of 15 Type Ia supernovae (SNe Ia) at redshift z > 1 (9 at 1.5 < z < 2.3) recently discovered in the CANDELS and CLASH Multi-Cycle Treasury programs using WFC3 on the Hubble Space Telescope. We combine these SNe Ia with a new compilation of 1050 SNe Ia, jointly calibrated and corrected for simulated survey biases to produce accurate distance measurements. We present unbiased constraints on the expansion rate at six redshifts in the range 0.07 < z < 1.5 based only on this combined SN Ia sample. The added leverage of our new sample at z > 1.5 leads to a factor of ~3 improvement in the determination of the expansion rate at z = 1.5, reducing its uncertainty to ~20%, a measurement of H(z=1.5)/H0=2.67 (+0.83,-0.52). We then demonstrate that these six measurements alone provide a nearly identical characterization of dark energy as the full SN sample, making them an efficient compression of the SN Ia data. The new sample of SNe Ia at z > 1 usefully distinguishes between alternative cosmological models and unmodeled evolution of the SN Ia distance indicators, placing empirical limits on the latter. Finally, employing a realistic simulation of a potential WFIRST SN survey observing strategy, we forecast optimistic future constraints on the expansion rate from SNe Ia.

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arXiv2017

Stellar Dynamics and Star-Formation Histories of z $\sim$ 1 Radio-loud Galaxies

We investigate the stellar kinematics and stellar populations of 58 radio-loud galaxies of intermediate luminosities (L$_{3 GHz}$ $>$ 10$^{23}$ W Hz$^{-1}$ ) at 0.6 < z < 1. This sample is constructed by cross-matching galaxies from the deep VLT/VIMOS LEGA-C spectroscopic survey with the VLA 3 GHz dataset. The LEGA-C continuum spectra reveal for the first time stellar velocity dispersions and age indicators of z $\sim$ 1 radio galaxies. We find that $z\sim 1$ radio-loud AGN occur exclusively in predominantly old galaxies with high velocity dispersions: $σ_*>$ 175 km s$^{-1}$, corresponding to black hole masses in excess of $10^8$ M$_{\odot}$. Furthermore, we confirm that at a fixed stellar mass the fraction of radio-loud AGN at z $\sim$ 1 is 5 - 10 times higher than in the local universe, suggesting that quiescent, massive galaxies at z $\sim$ 1 switch on as radio AGN on average once every Gyr. Our results strengthen the existing evidence for a link between high black-hole masses, radio loudness and quiescence at z $\sim$ 1.

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arXiv2017

Early Science with the Large Millimeter Telescope: Detection of dust emission in multiple images of a normal galaxy at $z>4$ lensed by a Frontier Fields cluster

We directly detect dust emission in an optically-detected, multiply-imaged galaxy lensed by the Frontier Fields cluster MACSJ0717.5+3745. We detect two images of the same galaxy at 1.1mm with the AzTEC camera on the Large Millimeter Telescope leaving no ambiguity in the counterpart identification. This galaxy, MACS071_Az9, is at z>4 and the strong lensing model (mu=7.5) allows us to calculate an intrinsic IR luminosity of 9.7e10 Lsun and an obscured star formation rate of 14.6 +/- 4.5 Msun/yr. The unobscured star formation rate from the UV is only 4.1 +/- 0.3 Msun/yr which means the total star formation rate (18.7 +/- 4.5 Msun/yr) is dominated (75-80%) by the obscured component. With an intrinsic stellar mass of only 6.9e9Msun, MACS0717_Az9 is one of only a handful of z>4 galaxies at these lower masses that is detected in dust emission. This galaxy lies close to the estimated star formation sequence at this epoch. However, it does not lie on the dust obscuration relation (IRX-beta) for local starburst galaxies and is instead consistent with the Small Magellanic Cloud (SMC) attenuation law. This remarkable lower mass galaxy showing signs of both low metallicity and high dust content may challenge our picture of dust production in the early Universe.

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arXiv2017

Predicting Quiescence: The Dependence of Specific Star Formation Rate on Galaxy Size and Central Density at 0.5<z<2.5

In this paper, we investigate the relationship between star formation and structure, using a mass-complete sample of 27,893 galaxies at $0.5 $0.5 dex in the central density threshold correlated with quiescence from $z\sim0.7-2.0$. Neither a compact size nor high-$n$ are sufficient to assess the likelihood of quiescence for the average galaxy; rather, the combination of these two parameters together with M$_{\star}$ results in a unique quenching threshold in central density/velocity.

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arXiv2017

The mass, colour, and structural evolution of today's massive galaxies since z~5

In this paper, we use stacking analysis to trace the mass-growth, colour evolution, and structural evolution of present-day massive galaxies ($\log(M_{*}/M_{\odot})=11.5$) out to $z=5$. We utilize the exceptional depth and area of the latest UltraVISTA data release, combined with the depth and unparalleled seeing of CANDELS to gather a large, mass-selected sample of galaxies in the NIR (rest-frame optical to UV). Progenitors of present-day massive galaxies are identified via an evolving cumulative number density selection, which accounts for the effects of merging to correct for the systematic biases introduced using a fixed cumulative number density selection, and find progenitors grow in stellar mass by $\approx1.5~\mathrm{dex}$ since $z=5$. Using stacking, we analyze the structural parameters of the progenitors and find that most of the stellar mass content in the central regions was in place by $z\sim2$, and while galaxies continue to assemble mass at all radii, the outskirts experience the largest fractional increase in stellar mass. However, we find evidence of significant stellar mass build up at $r<3~\mathrm{kpc}$ beyond $z>4$ probing an era of significant mass assembly in the interiors of present day massive galaxies. We also compare mass assembly from progenitors in this study to the EAGLE simulation and find qualitatively similar assembly with $z$ at $r<3~\mathrm{kpc}$. We identify $z\sim1.5$ as a distinct epoch in the evolution of massive galaxies where progenitors transitioned from growing in mass and size primarily through in-situ star formation in disks to a period of efficient growth in $r_{e}$ consistent with the minor merger scenario.

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arXiv2017

Near-infrared spectroscopy of 5 ultra-massive galaxies at 1.7 < z < 2.7

We present the results of a pilot near-infrared (NIR) spectroscopic campaign of five very massive galaxies ($\log(\text{M}_\star/\text{M}_\odot)>11.45$) in the range of $1.7<z<2.7$. We measure an absorption feature redshift for one galaxy at $z_\text{spec}=2.000\pm0.006$. For the remaining galaxies, we combine the photometry with the continuum from the spectra to estimate continuum redshifts and stellar population properties. We define a continuum redshift ($z_{\rm cont}$ ) as one in which the redshift is estimated probabilistically using EAZY from the combination of catalog photometry and the observed spectrum. We derive the uncertainties on the stellar population synthesis properties using a Monte Carlo simulation and examine the correlations between the parameters with and without the use of the spectrum in the modeling of the spectral energy distributions (SEDs). The spectroscopic constraints confirm the extreme stellar masses of the galaxies in our sample. We find that three out of five galaxies are quiescent (star formation rate of $\lesssim 1 M_\odot~yr^{-1}$) with low levels of dust obscuration ($A_{\rm V} < 1$) , that one galaxy displays both high levels of star formation and dust obscuration (${\rm SFR} \approx 300 M_\odot~{\rm yr}^{-1}$, $A_{\rm V} \approx 1.7$~mag), and that the remaining galaxy has properties that are intermediate between the quiescent and star-forming populations.

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arXiv2016

The Relation Between [OIII]/H$β$ and Specific Star Formation Rate in Galaxies at $z \sim 2$

Recent surveys have identified a seemingly ubiquitous population of galaxies with elevated [OIII]/H$β$ emission line ratios at $z > 1$, though the nature of this phenomenon continues to be debated. The [OIII]/H$β$ line ratio is of interest because it is a main component of the standard diagnostic tools used to differentiate between active galactic nuclei (AGN) and star-forming galaxies, as well as the gas-phase metallicity indicators $O_{23}$ and $R_{23}$. Here, we investigate the primary driver of increased [OIII]/H$β$ ratios by median-stacking rest-frame optical spectra for a sample of star-forming galaxies in the 3D-HST survey in the redshift range $z\sim1.4-2.2$. Using $N = 4220$ star-forming galaxies, we stack the data in bins of mass and specific star formation rates (sSFR) respectively. After accounting for stellar Balmer absorption, we measure [OIII]$\lambda5007$Å/H$β$ down to $\mathrm{M} \sim 10^{9.2} \ \mathrm{M_\odot}$ and sSFR $\sim 10^{-9.6} \ \mathrm{yr}^{-1}$, more than an order of magnitude lower than previous work at similar redshifts. We find an offset of $0.59\pm0.05$ dex between the median ratios at $z\sim2$ and $z\sim0$ at fixed stellar mass, in agreement with existing studies. However, with respect to sSFR, the $z \sim 2$ stacks all lie within 1$σ$ of the median SDSS ratios, with an average offset of only $-0.06\pm 0.05$. We find that the excitation properties of galaxies are tightly correlated with their sSFR at both $z\sim2$ and $z\sim0$, with a relation that appears to be roughly constant over the last 10 Gyr of cosmic time.

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arXiv2016

Ages of massive galaxies at $0.5 < z < 2.0$ from 3D-HST rest-frame optical spectroscopy

We present low-resolution near-infrared stacked spectra from the 3D-HST survey up to $z=2.0$ and fit them with commonly used stellar population synthesis models: BC03 (Bruzual & Charlot, 2003), FSPS10 (Flexible Stellar Population Synthesis, Conroy & Gunn 2010), and FSPS-C3K (Conroy, Kurucz, Cargile, Castelli, in prep). The accuracy of the grism redshifts allows the unambiguous detection of many emission and absorption features, and thus a first systematic exploration of the rest-frame optical spectra of galaxies up to $z=2$. We select massive galaxies ($\rm log(M_{*} / M_{\odot}) > 10.8$), we divide them into quiescent and star-forming via a rest-frame color-color technique, and we median-stack the samples in 3 redshift bins between $z=0.5$ and $z=2.0$. We find that stellar population models fit the observations well at wavelengths below $\rm 6500 Å$ rest-frame, but show systematic residuals at redder wavelengths. The FSPS-C3K model generally provides the best fits (evaluated with a $χ^2_{red}$ statistics) for quiescent galaxies, while BC03 performs the best for star-forming galaxies. The stellar ages of quiescent galaxies implied by the models, assuming solar metallicity, vary from 4 Gyr at $z \sim 0.75$ to 1.5 Gyr at $z \sim 1.75$, with an uncertainty of a factor of 2 caused by the unknown metallicity. On average the stellar ages are half the age of the Universe at these redshifts. We show that the inferred evolution of ages of quiescent galaxies is in agreement with fundamental plane measurements, assuming an 8 Gyr age for local galaxies. For star-forming galaxies the inferred ages depend strongly on the stellar population model and the shape of the assumed star-formation history.

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arXiv2016

Evidence for non-stellar rest-frame near-IR emission associated with increased star formation in galaxies at $z \sim 1$

We explore the presence of non-stellar rest-frame near-IR ($2-5 \ μ\mathrm{m}$) emission in galaxies at $z \sim 1$. Previous studies identified this excess in relatively small samples and suggested that such non-stellar emission, which could be linked to the $3.3 \ μ\mathrm{m}$ polycyclic aromatic hydrocarbons feature or hot dust emission, is associated with an increased star formation rate (SFR). In this Letter, we confirm and quantify the presence of an IR excess in a significant fraction of galaxies in the 3D-HST GOODS catalogs. By constructing a matched sample of galaxies with and without strong non-stellar near-IR emission, we find that galaxies with such emission are predominantly star-forming galaxies. Moreover, star-forming galaxies with an excess show increased mid- and far-IR and H$α$ emission compared to other star-forming galaxies without. While galaxies with a near-IR excess show a larger fraction of individually detected X-ray active galactic nuclei (AGNs), an X-ray stacking analysis, together with the IR-colors and H$α$ profiles, shows that AGNs are unlikely to be the dominant source of the excess in the majority of galaxies. Our results suggest that non-stellar near-IR emission is linked to increased SFRs and is ubiquitous among star-forming galaxies. As such, the near-IR emission might be a powerful tool to measure SFRs in the era of the James Webb Space Telescope.

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arXiv2015

Forming Compact Massive Galaxies

In this paper we study a key phase in the formation of massive galaxies: the transition of star forming galaxies into massive (M_stars~10^11 Msun), compact (r_e~1 kpc) quiescent galaxies, which takes place from z~3 to z~1.5. We use HST grism redshifts and extensive photometry in all five 3D-HST/CANDELS fields, more than doubling the area used previously for such studies, and combine these data with Keck MOSFIRE and NIRSPEC spectroscopy. We first confirm that a population of massive, compact, star forming galaxies exists at z~2, using K-band spectroscopy of 25 of these objects at 2.0<z<2.5. They have a median NII/Halpha ratio of 0.6, are highly obscured with SFR(tot)/SFR(Halpha)~10, and have a large range of observed line widths. We infer from the kinematics and spatial distribution of Halpha that the galaxies have rotating disks of ionized gas that are a factor of ~2 more extended than the stellar distribution. By combining measurements of individual galaxies, we find that the kinematics are consistent with a nearly Keplerian fall-off from V_rot~500 km/s at 1 kpc to V_rot~250 km/s at 7 kpc, and that the total mass out to this radius is dominated by the dense stellar component. Next, we study the size and mass evolution of the progenitors of compact massive galaxies. Even though individual galaxies may have had complex histories with periods of compaction and mergers, we show that the population of progenitors likely followed a simple inside-out growth track in the size-mass plane of d(log r_e) ~ 0.3 d(log M_stars). This mode of growth gradually increases the stellar mass within a fixed physical radius, and galaxies quench when they reach a stellar density or velocity dispersion threshold. As shown in other studies, the mode of growth changes after quenching, as dry mergers take the galaxies on a relatively steep track in the size-mass plane.

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arXiv2015

Illuminating a Dark Lens : A Type Ia Supernova Magnified by the Frontier Fields Galaxy Cluster Abell 2744

SN HFF14Tom is a Type Ia Supernova (SN) discovered at z = 1.3457 +- 0.0001 behind the galaxy cluster Abell 2744 (z = 0.308). In a cosmology-independent analysis, we find that HFF14Tom is 0.77 +- 0.15 magnitudes brighter than unlensed Type Ia SNe at similar redshift, implying a lensing magnification of mu_obs = 2.03 +- 0.29. This observed magnification provides a rare opportunity for a direct empirical test of galaxy cluster lens models. Here we test 17 lens models, 13 of which were generated before the SN magnification was known, qualifying as pure "blind tests". The models are collectively fairly accurate: 8 of the models deliver median magnifications that are consistent with the measured mu to within 1-sigma. However, there is a subtle systematic bias: the significant disagreements all involve models overpredicting the magnification. We evaluate possible causes for this mild bias, and find no single physical or methodological explanation to account for it. We do find that model accuracy can be improved to some extent with stringent quality cuts on multiply-imaged systems, such as requiring that a large fraction have spectroscopic redshifts. In addition to testing model accuracies as we have done here, Type Ia SN magnifications could also be used as inputs for future lens models of Abell 2744 and other clusters, providing valuable constraints in regions where traditional strong- and weak-lensing information is unavailable.

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arXiv2015

Multiple Images of a Highly Magnified Supernova Formed by an Early-Type Cluster Galaxy Lens

In 1964, Refsdal hypothesized that a supernova whose light traversed multiple paths around a strong gravitational lens could be used to measure the rate of cosmic expansion. We report the discovery of such a system. In Hubble Space Telescope imaging, we have found four images of a single supernova forming an Einstein cross configuration around a redshift z=0.54 elliptical galaxy in the MACS J1149.6+2223 cluster. The cluster's gravitational potential also creates multiple images of the z=1.49 spiral supernova host galaxy, and a future appearance of the supernova elsewhere in the cluster field is expected. The magnifications and staggered arrivals of the supernova images probe the cosmic expansion rate, as well as the distribution of matter in the galaxy and cluster lenses.

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arXiv2015

Not In Our Backyard: Spectroscopic Support for the CLASH z=11 Candidate MACS0647-JD

We report on our first set of spectroscopic Hubble Space Telescope observations of the z~11 candidate galaxy strongly lensed by the MACSJ0647.7+7015 galaxy cluster. The three lensed images are faint and we show that these early slitless grism observations are of sufficient depth to investigate whether this high-redshift candidate, identified by its strong photometric break at ~1.5 micron, could possibly be an emission line galaxy at a much lower redshift. While such an interloper would imply the existence of a rather peculiar object, we show here that such strong emission lines would clearly have been detected. Comparing realistic, two-dimensional simulations to these new observations we would expect the necessary emission lines to be detected at >5 sigma while we see no evidence for such lines in the dispersed data of any of the three lensed images. We therefore exclude that this object could be a low redshift emission line interloper, which significantly increases the likelihood of this candidate being a bona fide z~11 galaxy.

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arXiv2015

The Grism Lens-Amplified Survey from Space (GLASS). II. Gas-phase metallicity and radial gradients in an interacting system at z~2

We present spatially resolved gas-phase metallicity for a system of three galaxies at z=1.85 detected in the Grism Lens-Amplified Survey from Space (GLASS). The combination of HST's diffraction limit and strong gravitational lensing by the cluster MACS J0717+3745 results in a spatial resolution of ~200-300 pc, enabling good spatial sampling despite the intrinsically small galaxy sizes. The galaxies in this system are separated by 50-200 kpc in projection and are likely in an early stage of interaction, evidenced by relatively high specific star formation rates. Their gas-phase metallicities are consistent with larger samples at similar redshift, star formation rate, and stellar mass. We obtain a precise measurement of the metallicity gradient for one galaxy and find a shallow slope compared to isolated galaxies at high redshift, consistent with a flattening of the gradient due to gravitational interaction. An alternative explanation for the shallow metallicity gradient and elevated star formation rate is rapid recycling of metal-enriched gas, but we find no evidence for enhanced gas-phase metallicities which should result from this effect. Notably, the measured stellar masses log(M/Msun) = 7.2-9.1 probe to an order of magnitude below previous mass-metallicity studies at this redshift. The lowest mass galaxy has properties similar to those expected for Fornax at this redshift, indicating that GLASS is able to directly study the progenitors of local group dwarf galaxies on spatially resolved scales. Larger samples from the full GLASS survey will be ideal for studying the effects of feedback, and the time evolution of metallicity gradients. These initial results demonstrate the utility of HST spectroscopy combined with gravitational lensing for characterizing resolved physical properties of galaxies at high redshift.

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arXiv2014

A spectroscopic sample of massive, evolved z~2 galaxies: Implications for the evolution of the mass-size relation

We present deep, near-infrared HST/WFC3 grism spectroscopy and imaging for a sample of 14 galaxies at z~2 selected from a mass-complete photometric catalog in the COSMOS field. By combining the grism observations with photometry in 30 bands, we derive accurate constraints on their redshifts, stellar masses, ages, dust extinction and formation redshifts. We show that the slope and scatter of the z~2 mass-size relation of quiescent galaxies is consistent with the local relation, and confirm previous findings that the sizes for a given mass are smaller by a factor of two to three. Finally, we show that the observed evolution of the mass-size relation of quiescent galaxies between z=2 and 0 can be explained by quenching of increasingly larger star-forming galaxies, at a rate dictated by the increase in the number density of quiescent galaxies with decreasing redshift. However, we find that the scatter in the mass-size relation should increase in the quenching-driven scenario in contrast to what is seen in the data. This suggests that merging is not needed to explain the evolution of the median mass-size relation of massive galaxies, but may still be required to tighten its scatter, and explain the size growth of individual z=2 galaxies quiescent galaxies.

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arXiv2014

How dead are dead galaxies? Mid-Infrared fluxes of quiescent galaxies at redshift 0.3 < z < 2.5: implications for star formation rates and dust heating

We investigate the star formation rates of quiescent galaxies at high redshift (0.3 < z < 2.5) using 3D-HST WFC3 grism spectroscopy and Spitzer mid-infrared data. We select quiescent galaxies on the basis of the widely used UVJ color-color criteria. Spectral energy distribution fitting (rest frame optical and near-IR) indicates very low star formation rates for quiescent galaxies (sSFR ~ 10^-12 yr^-1). However, SED fitting can miss star formation if it is hidden behind high dust obscuration and ionizing radiation is re-emitted in the mid-infrared. It is therefore fundamental to measure the dust-obscured SFRs with a mid-IR indicator. We stack the MIPS-24um images of quiescent objects in five redshift bins centered on z = 0.5, 0.9, 1.2, 1.7, 2.2 and perform aperture photometry. Including direct 24um detections, we find sSFR ~ 10^-11.9 * (1+z)^4 yr^-1. These values are higher than those indicated by SED fitting, but at each redshift they are 20-40 times lower than those of typical star forming galaxies. The true SFRs of quiescent galaxies might be even lower, as we show that the mid-IR fluxes can be due to processes unrelated to ongoing star formation, such as cirrus dust heated by old stellar populations and circumstellar dust. Our measurements show that star formation quenching is very efficient at every redshift. The measured SFR values are at z > 1.5 marginally consistent with the ones expected from gas recycling (assuming that mass loss from evolved stars refuels star formation) and well above that at lower redshifts.

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arXiv2014

Dense cores in galaxies out to z=2.5 in SDSS, UltraVISTA, and the five 3D-HST/CANDELS fields

The dense interiors of massive galaxies are among the most intriguing environments in the Universe. In this paper we ask when these dense cores were formed and determine how galaxies gradually assembled around them. We select galaxies that have a stellar mass >3x10^10 Msun inside r=1 kpc out to z=2.5, using the 3D-HST survey and data at low redshift. Remarkably, the number density of galaxies with dense cores appears to have decreased from z=2.5 to the present. This decrease is probably mostly due to stellar mass loss and the resulting adiabatic expansion, with some contribution from merging. We infer that dense cores were mostly formed at z>2.5, consistent with their largely quiescent stellar populations. While the cores appear to form early, the galaxies in which they reside show strong evolution: their total masses increase by a factor of 2-3 from z=2.5 to z=0 and their effective radii increase by a factor of 5-6. As a result, the contribution of dense cores to the total mass of the galaxies in which they reside decreases from ~50% at z=2.5 to ~15% at z=0. Because of their early formation, the contribution of dense cores to the total stellar mass budget of the Universe is a strong function of redshift. The stars in cores with M_1kpc>3x10^10 Msun make up ~0.1% of the stellar mass density of the Universe today but 10%-20% at z~2, depending on their IMF. The formation of these cores required the conversion of ~10^11 Msun of gas into stars within ~1 kpc, while preventing significant star formation at larger radii.

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