Inger Jorgensen

The Gemini-North Multi-Object Spectrograph: Performance in imaging, long-slit, and multi-object spectroscopic modes

ABSTRACT Results of the commissioning of the first Gemini Multi‐Object Spectrograph (GMOS) are described. GMOS and the Gemini–North telescope act as a complete system to exploit a large 8 m aperture with improved image quality. Key GMOS design features such as the on‐instrument wave‐front sensor (OIWFS) and active flexure compensation system maintain very high image quality and stability, allowing precision observations of many targets simultaneously while reducing the need for frequent recalibration and reacquisition of targets. In this paper, example observations in imaging, long‐slit, and multiobject spectroscopic modes are presented and verified by comparison with data from the literature. The expected high throughput of GMOS is confirmed from standard star observations; it peaks at about 60% when imaging in the documentclass{aastex} usepackage{amsbsy} usepackage{amsfonts} usepackage{amssymb} usepackage{bm} usepackage{mathrsfs} usepackage{pifont} usepackage{stmaryrd} usepackage{textcomp} use...

The Gemini Deep Deep Survey, VII: the redshift evolution of the mass-metallicity relation

We have investigated the mass-metallicity (M-Z) relation using galaxies at 0.4 < z < 1.0 from the Gemini Deep Deep Survey (GDDS) and Canada-France Redshift Survey (CFRS). Deep K- and z-band photometry allowed us to measure stellar masses for 69 galaxies. From a subsample of 56 galaxies, for which metallicity of the interstellar medium is also measured, we identified a strong correlation between mass and metallicity for the first time in the distant universe. This was possible because of the larger baseline spanned by the sample in terms of metallicity (a factor of 7) and mass (a factor of 400) than in previous works. This correlation is much stronger and tighter than the luminosity-metallicity relation, confirming that stellar mass is a more meaningful physical parameter than luminosity. We find clear evidence for temporal evolution in the M-Z relation in the sense that at a given mass, a galaxy at z ~ 0.7 tends to have lower metallicity than a local galaxy of similar mass. We use the z ~ 0.1 Sloan Digital Sky Survey M-Z relation and a small sample of z ~ 2.3 Lyman break galaxies with known mass and metallicity to propose an empirical redshift-dependent M-Z relation. According to this relation the stellar mass and metallicity in small galaxies evolve for a longer time than they do in massive galaxies. This relation predicts that the generally metal-poor damped Lyα galaxies have stellar masses of the order of 108.8 M☉ (with a dispersion of 0.7 dex) all the way from z ~ 0.2 to 4. The observed redshift evolution of the M-Z relation can be reproduced remarkably well by a simple closed-box model in which the key assumption is an e-folding time for star formation that is higher or, in other words, a period of star formation that lasts longer in less massive galaxies than in more massive galaxies. Such a picture supports the downsizing scenario for galaxy formation.

RED NUGGETS AT z ∼ 1.5: COMPACT PASSIVE GALAXIES AND THE FORMATION OF THE KORMENDY RELATION

We present the results of Near-Infrared Camera and Multi-Object Spectrometer (NICMOS) imaging of a sample of 19 high-mass passively evolving galaxies with 1.2 < z < 2, taken primarily from the Gemini Deep Deep Survey (GDDS). Around 80% of galaxies in our GDDS sample have spectra dominated by stars with ages 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 size versus surface brightness parameter space which defines the Kormendy relation. Around one-third (3/10) of the massive red objects in the GDDS sample are extraordinarily compact, with effective radii under 1 kpc. 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 1.2 < z < 2. We refer to these compact galaxies as red nuggets, and note that similarly compact massive galaxies are completely absent in the nearby universe. We introduce a new stellar mass Kormendy relation (stellar mass density versus size) which we use to single out the effects of size evolution from those of luminosity and color evolution in stellar populations. The 1 < z < 2 passive galaxies have mass densities that are an order of magnitude larger then early-type galaxies today and are comparable to the compact distant red galaxies at 2 < z < 3. We briefly consider mechanisms for size evolution in contemporary models focusing on equal-mass mergers and adiabatic expansion driven by stellar mass loss. Neither of these mechanisms appears to be able to transform the high-redshift Kormendy relation into its local counterpart, leaving the origin and fate of these compact red nuggets unresolved.

Integral Field Spectroscopy with the Gemini Multiobject Spectrograph.I. Design, Construction, and Testing

The Gemini Multiobject Spectrograph (GMOS) installed on the Gemini-North telescope has a facility for integral field spectroscopy over the wavelength range 0.4-1.0 μm. GMOS is converted to this mode by the remote insertion of an integral field unit (IFU) into the beam in place of the masks used for the multiobject mode. With the IFU deployed, integral field spectroscopy is available over a fully filled contiguous field of 5 × 7 with a sampling of 02. A separate field of half the area, but otherwise identical, is also provided to improve background subtraction. The IFU contains 1500 lenslet-coupled fibers and is the first facility of any type for integral field spectroscopy employed on an 8-10 m telescope. We describe the design, construction, and testing of the GMOS IFU and present measurements of the throughput both in the laboratory and at the telescope. We compare these with a theoretical prediction made before construction started. All are in good agreement with each other, with the on-telescope throughput exceeding 60% (averaged over wavelength). A second paper will verify the scientific performance by comparison with existing one- and two-dimensional data sets.

Red nuggets at high redshift: structural evolution of quiescent galaxies over 10 Gyr of cosmic history

We present an analysis of the size growth seen in early-type galaxies over 10 Gyr of cosmic time. Our analysis is based on a homogeneous synthesis of published data from 16 spectroscopic surveys observed at similar spatial resolution, augmented by new measurements for galaxies in the Gemini Deep Deep Survey. In total, our sample contains structural data for 465 galaxies (mainly early-type) in the redshift range 0.2 < z < 2.7. The size evolution of passively evolving galaxies over this redshift range is gradual and continuous, with no evidence for an end or change to the process around z ~ 1, as has been hinted at by some surveys which analyze subsets of the data in isolation. The size growth appears to be independent of stellar mass, with the mass-normalized half-light radius scaling with redshift as Re ∝(1 + z)–1.62 ± 0.34. Surprisingly, this power law seems to be in good agreement with the recently reported continuous size evolution of UV-bright galaxies in the redshift range z ~ 0.5-3.5. It is also in accordance with the predictions from recent theoretical models.

Three Lyα emitters at z ≈ 6: Early GMOS/gemini data from the GLARE project

We report spectroscopic detection of three z ∼ 6 Lyα-emitting galaxies, in the vicinity of the Hubble Ultra Deep Field, from the early data of the Gemini Lyman Alpha at Reionisation Era (GLARE) project. Two objects, GLARE 3001 (z = 5.79) and GLARE 3011 (z = 5.94), are new detections and are fainter in z′ (z = 26.37 and 27.15) than any Lyman break galaxy previously detected in Lyα. A third object, GLARE 1042 (z = 5.83), has previously been detected in line emission from the ground; we report here a new spectroscopic continuum detection. Gemini/GMOS-South spectra of these objects, obtained using nod and shuffle, are presented together with a discussion of their photometric properties. All three objects were selected for spectroscopy via the i-drop Lyman break technique, the two new detections from the GOODS version 1.0 imaging data. The red i′-z′ colors and high equivalent widths of these objects suggest a high-confidence z > 5 Lyα identification of the emission lines. This brings the total number of known z > 5 galaxies within 9a of the Hubble Ultra Deep Field to four, of which three are at the same redshift (z = 5.8 within 2000 km s-1), suggesting the existence of a large-scale structure at this redshift.

THE GEMINI DEEP DEEP SURVEY. II. METALS IN STAR-FORMING GALAXIES AT REDSHIFT 1.3 < z < 2

The goal of the Gemini Deep Deep Survey (GDDS) is to study an unbiased sample of K 1.3. The selected objects have colors typical of irregular and Sbc galaxies. Strong [O II] emission indicates high star formation activity in the H II regions (star formation rate ~13-106 M☉ yr-1). The high signal-to-noise ratio composite spectrum shows strong ISM Mg II and Fe II absorption, together with weak Mn II and Mg I lines. The Fe II column density, derived using the curve of growth analysis, is log N = 15.54. This is considerably larger than typical values found in damped Lyα systems (DLAs) along QSO sight lines, where only 10 of 87 (~11%) have log N ≥ 15.2. High Fe II column densities are observed in the z = 2.72 Lyman break galaxy cB58 (log N 15.25) and in gamma-ray burst host galaxies (log N ~ 14.8-15.9). Given our measured Fe II column density and assuming a moderate iron dust depletion (δFe ~ 1 dex), we derive an optical dust extinction of AV ~ 0.6. If the H I column density is log N 0.2. The high completeness of the GDDS sample implies that these results are typical of star-forming galaxies in the 1 < z < 2 redshift range, an epoch that has heretofore been particularly challenging for observational programs.

SECONDARY PHOTOMETRIC STANDARD STARS FOR THE THUAN-GUNN AND THE JOHNSON-KRON-COUSINS SYSTEMS

CCD photometry is presented for 119 stars observed in the Thuan-Gunn photometric system (the passbands vgr). The sample includes 82 stars for which magnitudes in this system have not previously been published. Photometry in the Johnson-Kron-Cousins photometric system (BV or UBV) has been obtained for a sub-sample of 85 of the stars. Of those stars which are not primary standard stars for the Thuan-Gunn system 70 observed in Gunn r, 48 observed in Gunn g, and 37 observed in Gunn v have sufficient repeat measurements that they may be used as secondary standard stars for CCD photometry. The typical uncertainties for the magnitudes of these stars of 0.006m.

The Fundamental Plane for z = 0.8-0.9 Cluster Galaxies

We present the Fundamental Plane (FP) for 38 early-type galaxies in the two rich galaxy clusters RXJ0152.7-1357 (z=0.83) and RXJ1226.9+3332 (z=0.89), reaching a limiting magnitude of M_B =-19.8 mag in the rest frame of the clusters. While the zero point offset of the FP for these high redshift clusters relative to our low redshift sample is consistent with passive evolution with a formation redshift of z_form ~ 3.2, the FP for the high redshift clusters is not only shifted as expected for a mass-independent z_form, but rotated relative to the low redshift sample. Expressed as a relation between the galaxy masses and the mass-to-light ratios the FP is significantly steeper for the high redshift clusters than found at low redshift. We interpret this as a mass dependency of the star formation history, as has been suggested by other recent studies. The low mass galaxies (10^10.3 M_sun) have experienced star formation as recently as z ~ 1.35 (1.5 Gyr prior to their look back time), while galaxies with masses larger than 10^11.3 M_sun had their last major star formation episode at z > 4.5.

NGC 4314. IV. Photometry of Star Clusters with the Hubble Space Telescope: History of Star Formation in the Vicinity of a Nuclear Ring

Using Hubble Space Telescope (HST) WFPC2 images, we have obtained U, B, V, I, and Hα photometry for 76 star clusters in the nuclear star-forming ring of the barred spiral galaxy NGC 4314. These clusters are likely associated with an inner inner Lindblad resonance (IILR). The blue colors and Hα emission for most of these clusters imply very young ages of 1–15 Myr. Age estimates based on several reddening-free parameters indicate that the present epoch of star formation has lasted at least 30 Myr. By estimating the masses of stars in the clusters and comparing with the Hα luminosity, we conclude that a significant fraction of ongoing star formation in the nuclear ring of NGC 4314 occurs in clusters. The cluster masses identify these as young open clusters, not young globular clusters. Farther out in the galaxy, just exterior to the ring of young stars, previous ground-based observations revealed two symmetric stellar spiral arms that may be associated with an outer inner Lindblad resonance (OILR). With our HST data, we have revealed part of this structure and its colors in more detail. The spiral arm colors are consistent with stellar ages between 40 and 200 Myr. The age difference between the inner ring of young stars (IILR) and the larger oval-like feature containing the blue arms (OILR) supports an interpretation of the morphology of the nuclear region of NGC 4314 that requires a reservoir of gas that becomes more compact over time. We speculate that as the gas distribution becomes more centrally concentrated, it interacts with these two resonances. Each resonance triggers star formation, resulting in two distinct epochs of star formation.