Searcharxiv⌕ Search

arXiv subjects

Inger Jorgensen

Publications and source records attributed to Inger Jorgensen.

At least 19 recordsLinked to original sources
arXiv2021

Entering into the Wide Field Adaptive Optics Era on Maunakea

As part of the National Science Foundation funded "Gemini in the Era of MultiMessenger Astronomy" (GEMMA) program, Gemini Observatory is developing GNAO, a widefield adaptive optics (AO) facility for Gemini-North on Maunakea, the only 8m-class open-access telescope available to the US astronomers in the northern hemisphere. GNAO will provide the user community with a queue-operated Multi-Conjugate AO (MCAO) system, enabling a wide range of innovative solar system, Galactic, and extragalactic science with a particular focus on synergies with JWST in the area of time-domain astronomy. The GNAO effort builds on institutional investment and experience with the more limited block-scheduled Gemini Multi-Conjugate System (GeMS), commissioned at Gemini South in 2013. The project involves close partnerships with the community through the recently established Gemini AO Working Group and the GNAO Science Team, as well as external instrument teams. The modular design of GNAO will enable a planned upgrade to a Ground Layer AO (GLAO) mode when combined with an Adaptive Secondary Mirror (ASM). By enhancing the natural seeing by an expected factor of two, GLAO will vastly improve Gemini North's observing efficiency for seeing-limited instruments and strengthen its survey capabilities for multi-messenger astronomy.

astro-ph.IM↗
arXiv2019

The Gemini/HST Galaxy Cluster Project: Environment Effects on the Stellar Populations in the Lynx Clusters at z=1.27

Few detailed investigations of stellar populations in passive galaxies beyond z~1 are based on deep spectroscopic observations, due to the difficulty in obtaining such data. We present a study of stellar populations, structure, and mass-to-light ratios of a large sample of bulge-dominated galaxies in the two z=1.27 clusters Lynx E and Lynx W, based on deep ground-based optical spectroscopy combined with imaging from Hubble Space Telescope. We find that Lynx E has a well-defined core of red passive galaxies, while Lynx W lacks such a core. If all the sample galaxies evolve similarly in size from z=1.27 to the present, the data allow only 0.1 dex size-growth at a fixed dynamical mass. However, to link the Lynx central galaxies to brightest cluster galaxies similar to those of low redshift clusters, the Lynx galaxies would have to grow by at least a factor five, possibly through major merging. The mass-to-light ratios and the Balmer absorption lines of the Lynx galaxies are consistent with passive evolution of the stellar populations from z=1.27 to the present and support ages of 1--3 Gyr. The galaxies in the outskirts of the clusters contain younger stellar populations than found in the cluster cores. However, when evolved passively to z~0 both populations are consistent with the observed populations in the Coma cluster galaxies. The bulge-dominated emission line galaxies in the clusters are dominated by stellar populations with sub-solar metallicities. Thus, additional enrichment of these is required to produce Coma-like stellar populations by z~0.

astro-ph.GA↗
arXiv2018

The Gemini/HST Galaxy Cluster Project: Stellar Populations in the Low Redshift Reference Cluster Galaxies

In order to study stellar populations and galaxy structures at intermediate and high redshift (z=0.2-2.0) and link these properties to those of low redshift galaxies, there is a need for well-defined local reference samples. Especially for galaxies in massive clusters, such samples are often limited to the Coma cluster galaxies. We present consistently calibrated velocity dispersions and absorption line indices for galaxies in the central 2 R500 x 2 R500 of four massive clusters at z<0.1: Abell 426/Perseus, Abell 1656/Coma, Abell 2029, and Abell 2142. The measurements are based on data from Gemini Observatory, McDonald Observatory, and the Sloan Digital Sky Survey. For bulge-dominated galaxies the samples are 95 percent complete in Perseus and Coma, and 74 percent complete in A2029 and A2142, to a limit of M_Babs <= -18.5 mag. The data serve as the local reference for our studies of galaxy populations in the higher redshift clusters that are part of the Gemini/HST Galaxy Cluster Project (GCP). We establish the scaling relations between line indices and velocity dispersions as reference for the GCP. We derive stellar population parameters ages, metallicities [M/H], and abundance ratios from line indices, both averaged in bins of velocity dispersion, and from individual measurements for galaxies in Perseus and Coma. The zero points of relations between the stellar population parameters and the velocity dispersions limit the allowed cluster-to-cluster variation of the four clusters to +-0.08 dex in age, +-0.06 dex in [M/H], +-0.07 dex in [CN/Fe], and +-0.03 dex in [Mg/Fe].

astro-ph.GA↗
arXiv2018

The Gemini/HST galaxy cluster project: Redshift 0.2-1.0 cluster sample, X-ray data and optical photometry catalog

The Gemini/HST Galaxy Cluster Project (GCP) covers 14 z=0.2-1.0 clusters with X-ray luminosity of L_500 >= 10^44 ergs/s in the 0.1-2.4 keV band. In this paper we provide homogeneously calibrated X-ray luminosities, masses and radii, and we present the complete catalog of the ground-based photometry for the GCP clusters. The clusters were observed with Gemini North or South in three or four of the optical passbands g', r', i' and z'. The photometric catalog includes consistently calibrated total magnitudes, colors, and geometrical parameters. The photometry reaches ~25 mag in the passband closest to rest frame B-band. We summarize comparisons of our photometry with data from the Sloan Digital Sky Survey. We describe the sample selection for our spectroscopic observations, and establish the calibrations to obtain rest frame magnitudes and colors. Finally, we derive the color-magnitude relations for the clusters and briefly discuss these in the context of evolution with redshift. Consistent with our results based on spectroscopic data, the color-magnitude relations support passive evolution of the red-sequence galaxies. The absence of change in the slope with redshift, constrains the allowable age variation along the red sequence to <0.05 dex between the brightest cluster galaxies and those four magnitudes fainter. The paper serves as the main reference for the GCP cluster and galaxy selection, X-ray data and ground-based photometry.

astro-ph.GA↗
arXiv2017

Galaxy populations in massive z=0.2-0.9 clusters: I. Analysis of spectroscopy

We present an analysis of stellar populations in passive galaxies in seven massive X-ray clusters at z=0.19-0.89. Based on absorption line strengths measured from our high signal-to-noise spectra, the data support primarily passive evolution of the galaxies. We use the scaling relations between velocity dispersions and the absorption line strengths to determine representative mean line strengths for the clusters. From the age determinations based on the line strengths (and stellar population models), we find a formation redshift of z_form=1.96(-0.19,+0.24). Based on line strength measurements from high signal-to-noise composite spectra of our data, we establish the relations between velocity dispersion, ages, metallicities [M/H] and abundance ratios [alpha/Fe] as a function of redshift. The [M/H]-velocity dispersion and [alpha/Fe]-velocity dispersion relations are steep and tight. The age-velocity dispersion relation is flat, with zero point changes reflecting passive evolution. The scatter in all three parameters are within 0.08-0.15 dex at fixed velocity dispersions, indicating a large degree of synchronization in the evolution of the galaxies. We find indication of cluster-to-cluster differences in metallicities and abundance ratios. However, variations in stellar populations with the cluster environment can only account for a very small fraction of the intrinsic scatter in the scaling relations. Thus, within these very massive clusters the main driver of the properties of the stellar populations in passive galaxies appears to be the galaxy velocity dispersion.

astro-ph.GA↗
arXiv2015

Low Angular Momentum in Clumpy, Turbulent Disk Galaxies

We measure the stellar specific angular momentum jstar=Jstar/Mstar in four nearby (z~0.1) disk galaxies that have stellar masses Mstar near the break M* of the galaxy mass function, but look like typical star-forming disks at z~2 in terms of their low stability (Q~1), clumpiness, high ionized gas dispersion (40-50 km/s), high molecular gas fraction (20-30%) and rapid star formation (~20 Msun/yr). Combining high-resolution (Keck-OSIRIS) and large-radius (Gemini-GMOS) spectroscopic maps, only available at low z, we discover that these targets have about three times less stellar angular momentum than typical local spiral galaxies of equal stellar mass and bulge fraction. Theoretical considerations show that this deficiency in angular momentum is the main cause of their low stability, while the high gas fraction plays a complementary role. Interestingly, the low jstar values of our targets are similar to those expected in the M*-population at higher z from the approximate theoretical scaling jstar~(1+z)^(-1/2) at fixed Mstar. This suggests that a change in angular momentum, driven by cosmic expansion, is the main cause for the remarkable difference between clumpy M*-disks at high z (which likely evolve into early-type galaxies) and mass-matched local spirals.

astro-ph.GA↗
arXiv2014

RXJ0848.6+4453: The Evolution of Galaxy Sizes and Stellar Populations in a z=1.27 Cluster

RXJ0848.6+4453 (Lynx W) at redshift 1.27 is part of the Lynx Supercluster of galaxies. Our analysis of stellar populations and star formation history in the cluster covers 24 members and is based on deep optical spectroscopy from Gemini North and imaging data from HST. Focusing on the 13 bulge-dominated galaxies for which we can determine central velocity dispersions, we find that these show a smaller evolution of sizes and velocity dispersions than reported for field galaxies and galaxies in poorer clusters. The galaxies in RXJ0848.6+4453 populate the Fundamental Plane similar to that found for lower redshift clusters with a zero point offset corresponding to an epoch of last star formation at z_form= 1.95+-0.2. The spectra of the galaxies in RXJ0848.6+4453 are dominated by young stellar populations at all galaxy masses and in many cases show emission indicating low level on-going star formation. The average age of the young stellar populations (estimated from H-zeta) is consistent with a major star formation episode 1-2 Gyr prior, which in turn agrees with z_form=1.95. Galaxies dominated by young stellar populations are distributed throughout the cluster. We speculate that low level star formation has not yet been fully quenched in the center of this cluster may be because the cluster is significantly poorer than other clusters previously studied at similar redshifts, which appear to have very little on-going star formation in their centers.

astro-ph.GA↗
arXiv2013

Stellar populations and evolution of early-type cluster galaxies: Constraints from optical imaging and spectroscopy of z=0.5-0.9 galaxy clusters

We present an analysis of stellar populations and evolutionary history of galaxies in three similarly rich galaxy clusters MS0451.6-0305 (z=0.54), RXJ0152.7-1357 (z=0.83), and RXJ1226.9+3332 (z=0.89); based on high S/N ground-based optical spectroscopy and HST imaging for 17-34 members in each cluster. We find no indication of evolution of sizes or velocity dispersions with redshift at a given dynamical galaxy mass. We establish the Fundamental Plane (FP) and scaling relations between absorption line indices and velocity dispersions. We confirm the steeper FP at z=0.86 compared to the low redshift FP, indicating (under the assumption of passive evolution) the formation redshift, z_form, depends on the galaxy velocity dispersion (or mass). z_form varies from z_form=1.24+-0.05 at velocity dispersion of 125 km/s to 1.95+-0.25 at 225 km/s. The three clusters and the low redshift sample follow similar scaling relations between absorption line indices and velocity dispersions. The strength of the higher order Balmer lines Hdelta and Hgamma implies z_form>2.8. From the line strengths we find that [M/H] for MS0451.6-0305 is about 0.2 dex below that of the other clusters, and confirm our previous result that [alpha/Fe] for RXJ0152.7-1357 is about 0.3 dex higher than that of the other clusters. These differences between the high-redshift clusters and the low redshift sample are inconsistent with a passive evolution scenario for early-type cluster galaxies over the redshift interval studied. (abridged)

astro-ph.CO↗
arXiv2012

Suppression of Star Formation in the central 200 kpc of a z = 1.4 Galaxy Cluster [Erratum added]

We present the results of an extended narrow-band Hα study of the massive galaxy cluster XMMU J2235.3-2557 at z = 1.39. This paper represents a follow up study to our previous investigation of star-formation in the cluster centre, extending our analysis out to a projected cluster radius of 1.5 Mpc. Using the Near InfraRed Imager and Spectrograph (NIRI) on Gemini North we obtained deep H narrow-band imaging corresponding to the rest-frame wavelength of Hα at the cluster's redshift. We identify a total of 163 potential cluster members in both pointings, excluding stars based on their near-IR colours derived from VLT/HAWK-I imaging. Of these 163 objects 14 are spectroscopically confirmed cluster members, and 20% are excess line-emitters. We find no evidence of star formation activity within a radius of 200 kpc of the brightest cluster galaxy in the cluster core. Dust-corrected star formation rates (SFR) of excess emitters outside this cluster quenching radius, RQ \sim 200 kpc, are on average = 2.7 \pm 1.0 M\odot yr-1, but do not show evidence of increasing star-formation rates toward the extreme 1.5 Mpc radius of the cluster. No individual cluster galaxy exceeds an SFR of 6 M\odot yr-1 . Massive galaxies (log M\ast /M\odot > 10.75) all have low specific SFRs (SSFRs, i.e. SFR per unit stellar mass). At fixed stellar mass, galaxies in the cluster centre have lower SSFRs than the rest of the cluster galaxies, which in turn have lower SSFRs than field galaxies at the same redshift by a factor of a few to 10. For the first time we can demonstrate through measurements of individual SFRs that already at very early epochs (at an age of the Universe of \sim4.5 Gyr) the suppression of star-formation is an effect of the cluster environment which persists at fixed galaxy stellar mass. [Erratum added after the original paper]

astro-ph.CO↗
arXiv2012

GNOMOS: The Gemini NIR-Optical Multi Object Spectrograph

This paper is a response to a call for white papers solicited by Gemini Observatory and its Science and Technology Advisory Committee, to help define the science case and requirements for a new Gemini instrument, envisaged to consist of a single-object spectrograph at medium resolution simultaneously covering optical and near-infrared wavelengths. In this white paper we discuss the science case for an alternative new instrument, consisting instead of a multi-object, medium-resolution, high-throughput spectrograph, covering simultaneously the optical and near-infrared slices of the electromagnetic spectrum. We argue that combination of wide wavelength coverage at medium resolution with moderate multiplexing power is an innovative path that will enable the pursuit of fundamental science questions in a variety of astrophysical topics, without compromise of the science goals achievable by single-object spectroscopy on a wide baseline. We present a brief qualitative discussion of the main features of a notional hardware design that could conceivably make such an instrument viable.

astro-ph.IM↗
arXiv2010

Star Formation in the XMMU J2235.3-2557 Galaxy Cluster at z=1.39

We present the first results of a narrow-band photometric study of the massive galaxy cluster XMMU J2235.3-2557 at z=1.39. We obtained deep $H$ narrow-band imaging with NIRI on Gemini North, corresponding to H-alpha emission at the cluster's redshift. Our sample consists of 82 galaxies within a radius of ~500 kpc, ten of which are spectroscopically confirmed cluster members. Sixteen galaxies are identified as excess line-emitters. Among just the excess line-emitting galaxies we find an average SFR of 3.6 +/- 1.3 Msun/yr. For spectroscopically confirmed cluster members we find a correlation between H broad-band magnitude and SFR such that brighter galaxies have lower SFRs. The probability that SFR and magnitude of confirmed members are uncorrelated is 0.7%. We also find a correlation between SFR and distance from the cluster centre for both confirmed and excess line-emitting candidate members, with a probability of 5% for there to be no correlation among confirmed members. All excess line-emitting candidate cluster members are located outside a radius of 200 kpc. We conclude that star formation is effectively shut off within the central 200 kpc radius (R_QUENCH ~ 200 kpc) of this massive galaxy cluster at z=1.39, when the universe was only 4.5 Gyr old.

astro-ph.CO↗
arXiv2010

Mass dependent Evolution of Field Early-Type Galaxies Since z=1

We present the Fundamental Plane (FP) of field early-type galaxies at 0.5<z<1.0. Our project is a continuation of our efforts to understand the formation and evolution of early-type galaxies in different environments. The target galaxies were selected from the comprehensive and homogeneous data set of the Gemini/HST Galaxy Cluster Project. The distant field early-type galaxies follow a steeper FP relation compared to the local FP. The change in the slope of the FP can be interpreted as a mass-dependent evolution. Similar results have been found for cluster early-type galaxies in high redshift galaxy clusters at 0.8<z<1. Therefore, the slope change of the FP appears to be independent of the environment of the galaxies.

astro-ph.CO↗
arXiv2009

The Evolution of Cluster Early-Type Galaxies over the Past 8 Gyr

We present the Fundamental Plane (FP) of early-type galaxies in the clusters of galaxies RXJ1415.1+3612 at z=1.013. This is the first detailed FP investigation of cluster early-type galaxies at redshift z=1. The distant cluster galaxies follow a steeper FP relation compared to the local FP. The change in the slope of the FP can be interpreted as a mass-dependent evolution. To analyse in more detail the galaxy population in high redshift galaxy clusters at 0.8 2x10^{11}M_{\sun}) the bulk of their stellar populations have been formed earlier z_{form}>~1.6. Our results confirm previous findings by Jorgensen et al. This suggests that the less massive galaxies in the distant clusters have much younger stellar populations than their more massive counterparts. One explanation is that low-mass cluster galaxies have experienced more extended star formation histories with more frequent bursts of star formation with shorter duration compared to the formation history of high-mass cluster galaxies.

astro-ph.CO↗
arXiv2009

The Gemini/HST Cluster Project: Structural and Photometric Properties of Galaxies in Three z =0.28-0.89 Clusters

We present the data processing and analysis techniques we are using to determine structural and photometric properties of galaxies in our Gemini/HST Galaxy Cluster Project sample. The goal of this study is to understand cluster galaxy evolution in terms of scaling relations and structural properties of cluster galaxies at redshifts 0.15 < z < 1.0. To derive parameters such as total magnitude, half-light radius, effective surface brightness, and Sersic n, we fit r^{1/4} law and Sersic function 2-D surface brightness profiles to each of the galaxies in our sample. Using simulated galaxies, we test how the assumed profile affects the derived parameters and how the uncertainties affect our Fundamental Plane results. We find that while fitting galaxies which have Sersic index n < 4 with r^{1/4} law profiles systematically overestimates the galaxy radius and flux, the combination of profile parameters that enter the Fundamental Plane has uncertainties that are small. Average systematic offsets and associated random uncertainties in magnitude and log r_e for n > 2 galaxies fitted with r^{1/4} law profiles are -0.1+-0.3 and 0.1+-0.2 respectively. The combination of effective radius and surface brightness, log r_e - βlog _e, that enters the Fundamental Plane produces offsets smaller than -0.02+-0.10. This systematic error is insignificant and independent of galaxy magnitude or size. A catalog of photometry and surface brightness profile parameters is presented for three of the clusters in our sample, RX J0142.0+2131, RX J0152.7-1357, and RX J1226.9+3332 at redshifts 0.28, 0.83, and 0.89 respectively.

astro-ph.CO↗
arXiv2009

Red Nuggets at z~1.5: Compact passive galaxies and the formation of the Kormendy Relation

We present the results of NICMOS imaging of a sample of 16 high mass passively evolving galaxies with 1.3 1 Gyr. Our rest-frame R-band images show that most of these objects have compact regular morphologies which follow the classical R^1/4 law. These galaxies scatter along a tight sequence in the Kormendy relation. Around one-third of the massive red objects are extraordinarily compact, with effective radii under one kiloparsec. Our NICMOS observations allow the detection of such systems more robustly than is possible with optical (rest-frame UV) data, and while similar systems have been seen at z>2, this is the first time such systems have been detected in a rest-frame optical survey at 1.3

astro-ph↗
arXiv2008

Calibration of photometry from the Gemini Multi-Object Spectrograph on Gemini North

All available observations of photometric standard stars obtained with the Gemini Multi-Object Spectrograph at Gemini North in the period from August 2001 to December 2003 have been used to establish the calibrations for photometry obtained with the instrument. The calibrations presented in this paper are based on significantly more photometric standard star observations than usually used by the individual users. Nightly photometric zero points as well as color terms are determined. The color terms are expected to be valid for all observations taken prior to UT 2004 November 21 at which time the Gemini North primary mirror was coated with silver instead of aluminum. While the nightly zero points are accurate to 0.02 mag or better (random errors), the accuracy of the calibrations is limited by systematic errors from so-called "sky concentration", an effect seen in all focal reducer instruments. We conclude that an accuracy of 0.035 to 0.05 mag can be achieved by using calibrations derived in this paper. The color terms are strongest for very red objects, e.g. for objects with (r'-z')=3.0 the resulting z' magnitudes will be ~0.35 mag too bright if the color term is ignored. The calibrations are of importance to the large Gemini user community with data obtained prior to UT 2004 November 21, as well as future users of achive data from this period in time.

astro-ph↗
arXiv2007

The Gemini Deep Deep Survey: VIII. When Did Early-type Galaxies Form?

We have used the Hubble Space Telescope's Advanced Camera for Surveys (Ford et al. 2003) to measure the cumulative mass density in morphologically-selected early-type galaxies over the redshift range 0.8 < z < 1.7. Our imaging data set covers four well-separated sight-lines, and is roughly intermediate (in terms of both depth and area) between the GOODS/GEMS imaging data, and the images obtained in the Hubble Deep Field campaigns. Our images contain 144 galaxies with ultra-deep spectroscopy obtained as part of the Gemini Deep Deep Survey. These images have been analyzed using a new purpose-written morphological analysis code which improves the reliability of morphological classifications by adopting a 'quasi-Petrosian' image thresholding technique. We find that at z \~ 1 about 80% of the stars living in the most massive galaxies reside in early-type systems. This fraction is similar to that seen in the local Universe. However, we detect very rapid evolution in this fraction over the range 0.8 < z < 1.7, suggesting that over this redshift range the strong morphology-mass relationship seen in the nearby Universe is beginning to fall into place. By comparing our images to published spectroscopic classifications, we show that little ambiguity exists in connecting spectral classes to morphological classes for spectroscopically quiescent systems. However, the mass density function of early-type galaxies is evolving more rapidly than that of spectroscopically quiescent systems, which we take as further evidence that we are witnessing the formation of massive early-type galaxies over the 0.8 < z < 1.7 redshift range.

astro-ph↗
arXiv2006

When do early-type galaxies form?

We have used the Hubble Space Telescope's Advanced Camera for Surveys to measure the mass density function of morphologically selected early-type galaxies in the Gemini Deep Deep Survey fields, over the redshift range 0.9 < z < 1.6. Our imaging data set covers four well-separated sight-lines, and is roughly intermediate (in terms of both depth and area) between the GOODS/GEMS imaging data, and the images obtained in the Hubble Deep Field campaigns. Our images contain 144 galaxies with ultra-deep spectroscopy, and they have been analyzed using a new purpose-written morphological analysis code which improves the reliability of morphological classifications by adopting a 'quasi-petrosian' image thresholding technique. We find that at z = 1 approximately 70% of the stars in massive galaxies reside in early-type systems. This fraction is remarkably similar to that seen in the local Universe. However, we detect very rapid evolution in this fraction over the range 1.0 < z < 1.6, suggesting that in this epoch the strong color-morphology relationship seen in the nearby Universe is beginning to fall into place.

astro-ph↗