arXiv subjects

Alan F. M. Moorwood

Publications and source records attributed to Alan F. M. Moorwood.

6 recordsLinked to original sources

arXiv2006

What do we learn from IRAC observations of galaxies at 2 < z < 3.5?

We analyze very deep HST, VLT and Spitzer photometry of galaxies at 2 2 galaxies. The estimated distributions of these properties do not change significantly when adding IRAC data to the UBVIJHK photometry. However, for individual galaxies the addition of IRAC can improve the constraints on the stellar populations, especially for red galaxies: uncertainties in stellar mass decrease by a factor of 2.7 for red (U-V > 1) galaxies, but only by a factor of 1.3 for blue (U-V < 1) galaxies. We find a similar color-dependence of the improvement for estimates of age and dust extinction. In addition, the improvement from adding IRAC depends on the availability of full near-infrared JHK coverage; if only K-band were available, the mass uncertainties of blue galaxies would decrease by a more substantial factor 1.9. Finally, we find that a trend of galaxy color with stellar mass is already present at z>2. The most massive galaxies at high redshift have red rest-frame U-V colors compared to lower mass galaxies even when allowing for complex star formation histories.

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arXiv2003

H-alpha Spectroscopy of Galaxies at z>2: Kinematics and Star Formation

We present near-infrared spectroscopy of H-alpha emission lines in a sample of 16 star-forming galaxies at redshifts 2.0 4e10 M_sun. One-dimensional velocity dispersions for the 16 galaxies range from ~50 to ~260 km/s, and in cases where we have both virial masses implied by the velocity dispersions and dynamical masses derived from the spatially extended emission lines, they are in rough agreement. We compare our kinematic results to similar measurements made at z~3, and find that both the observed rotational velocities and velocity dispersions tend to be larger at z~2 than at z~3. We find a mean SFR_H-alpha of 16 M_sun/yr and an average SFR_H-alpha/SFR_UV ratio of 2.4, without correcting for extinction. We see moderate evidence for an inverse correlation between the UV continuum luminosity and the ratio SFR_H-alpha/SFR_UV, such as might be observed if the UV-faint galaxies suffered greater extinction. We discuss the effects of dust and star formation history on the SFRs, and conclude that extinction is the most likely explanation for the discrepancy between the two SFRs.

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arXiv2001

Probing the evolution of galaxies using redshifted H-alpha emission

In this paper we review the present status and implications of H-alpha surveys at various redshifts. With the advent of sensitive wide-format near-infrared detectors on large telescopes, deep and extensive H-alpha surveys are now feasible to redshift z~2.5. The cosmic star formation history can therefore be traced out to this redshift using H-alpha alone, avoiding complications arising from the comparison of different tracers at different redshifts. The H-alpha surveys to date confirm the rapid increase in luminosity density from z=0 out to z=1, and show that this increase flattens off at higher redshifts, remaining approximately constant out to at least z~2.2. We also discuss the prospects for determining the masses of high redshift galaxies based on emission lines. A set of high-quality H-alpha rotation curves of samples of disk galaxies at a number of different redshifts would allow a study of the evolution of the Tully-Fisher relation and address fundamental issues in disk galaxy formation. Such a program remains challenging even with present-day large telescopes.

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arXiv2001

The Rest Frame Optical Spectra of Lyman Break Galaxies: Star Formation, Extinction, Abundances, and Kinematics

We present the first results of a spectroscopic survey of Lyman break galaxies in the near-infrared aimed at detecting the emission lines of [O II], [O III], and Hbeta from the H II regions of star forming galaxies at z = 3. From observations of 19 objects with the Keck and VLT telescopes, we reach the following main conclusions. Contrary to expectations, the star formation rates deduced from the Hbeta luminosity are on average no larger than those implied by the stellar continuum at 1500 A; presumably any differential extinction between rest-frame optical and UV is small compared with the relative uncertainties in the calibrations of these two star formation tracers. For the galaxies in our sample, the abundance of O can only be determined to within one order of magnitude. Even so, it seems well established that LBGs are the most metal-enriched structures at z = 3, apart from QSOs, with abundances greater than about 1/10 solar. They are also significantly overluminous for their metallicities; this is probably an indication that their mass-to-light ratios are small compared with present-day galaxies. At face value their velocity dispersions, sigma = 50 - 115 km/s imply virial masses of about 10^{10} solar masses within half-light radii of 2.5 kpc. However, we are unable to establish if the widths of the emission lines do reflect the motions of the H II regions within the gravitational potential of the galaxies, even though in two cases we see hints of rotation curves. All 19 LBGs observed show evidence for galactic-scale superwinds; such outflows are important for regulating star formation, distributing metals over large volumes, and allowing Lyman continuum photons to escape and ionize the IGM.

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arXiv2001

Deep Observations of Lyman Break Galaxies

We summarise the main results of recent work on the Lyman break galaxy population which takes advantage of newly commissioned instrumentation on the VLT and Keck telescopes to push the detection of these objects to new wavelengths and more sensitive limits. We focus in particular on near-infrared observations targeted at detecting emission lines of [O II], [O III], and H-beta and on the first tentative detection of Lyman continuum emission from star forming galaxies at z = 3.

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arXiv2000

Halpha emitting galaxies and the cosmic star formation rate at z = 2.2

About 10 candidate Halpha emitting galaxies at z = 2.2 have been detected in a 2.1 um narrow band imaging survey covering an area of 100 sq. arcmin including the WFPC2 and STIS fields in the Hubble Deep Field South. Six of these have subsequently been confirmed spectroscopically using ISAAC at the ESO VLT. Star formation rates of the individual galaxies derived from their Halpha fluxes are 20-35 Msolar/yr, without any correction for extinction, whereas SFRs derived from their rest frame UV continuum fluxes are up to a factor of 4 lower - consistent with lower extinction to Halpha. Velocity dispersions are typically ~ 100km/s and one galaxy, observed under the most favorable conditions, shows a rotation curve with a terminal velocity ~ 140 km/s at ~ 3kpc radius which is within the range observed for nearby spiral galaxies. These thus appear to be relatively massive systems at high redshift. Comparison with the HST NICMOS grism Halpha survey of Yan et al. (1999) reveals little or no evolution in the Halpha luminosity function between z ~ 1.3 and 2.2. The inferred star formation rate density of 0.12 Msolar/Mpc^3/yr at z = 2.2 is also equal to that at z ~ 3-4.5 derived by Steidel et al.(1999) from extinction corrected UV continuum fluxes.

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