Evolution of Lyman Alpha Galaxies: Stellar Populations at z ~ 0.3

We present the results of a stellar population analysis of 30 Lyman alpha emitting galaxies (LAEs) at z ~ 0.3, previously discovered with the Galaxy Evolution Explorer (GALEX). With a few exceptions, we can accurately fit model spectral energy distributions to these objects, representing the first time this has been done for a large sample of LAEs at z < 3, a gap of ~ 8 Gyr in the history of the Universe. From the 26/30 LAEs which we can fit, we find an age and stellar mass range of 200 Myr - 10 Gyr and 10^9 - 10^11 Msol, respectively. These objects thus appear to be significantly older and more massive than LAEs at high-redshift. We also find that these LAEs show a mild trend towards higher metallicity than those at high redshift, as well as a tighter range of dust attenuation and interstellar medium geometry. These results suggest that low-redshift LAEs have evolved significantly from those at high redshift.Comment: Accepted for publication in the Astrophysical Journal. Replaced with accepted version. Eight pages, four figures, in emulateapj forma

Herschel Extreme Lensing Line Observations: Dynamics of two strongly lensed star forming galaxies near redshift z = 2

We report on two regularly rotating galaxies at redshift z=2, using high resolution spectra of the bright [CII] 158 micron emission line from the HIFI instrument on the Herschel Space Observatory. Both SDSS090122.37+181432.3 ("S0901") and SDSS J120602.09+514229.5 ("the Clone") are strongly lensed and show the double-horned line profile that is typical of rotating gas disks. Using a parametric disk model to fit the emission line profiles, we find that S0901 has a rotation speed v sin(i) = 120 +/- 7 km/s and gas velocity dispersion sigma < 23 km/s. The best fitting model for the Clone is a rotationally supported disk having v sin(i) = 79 +/- 11 km/s and sigma < 4km/s. However the Clone is also consistent with a family of dispersion-dominated models having sigma = 92 +/- 20 km/s. Our results showcase the potential of the [CII] line as a kinematic probe of high redshift galaxy dynamics: [CII] is bright; accessible to heterodyne receivers with exquisite velocity resolution; and traces dense star-forming interstellar gas. Future [CII] line observations with ALMA would offer the further advantage of spatial resolution, allowing a clearer separation between rotation and velocity dispersion.Comment: 20 pages, 4 figures; in press at The Astrophysical Journa

Galactic winds and stellar populations in Lyman α\alpha emitting galaxies at z ~ 3.1

We present a sample of 33 spectroscopically confirmed z ~ 3.1 Ly$\alpha$-emitting galaxies (LAEs) in the Cosmological Evolution Survey (COSMOS) field. This paper details the narrow-band survey we conducted to detect the LAE sample, the optical spectroscopy we performed to confirm the nature of these LAEs, and a new near-infrared spectroscopic detection of the [O III] 5007 \AA\ line in one of these LAEs. This detection is in addition to two [O III] detections in two z ~ 3.1 LAEs we have reported on previously (McLinden et al 2011). The bulk of the paper then presents detailed constraints on the physical characteristics of the entire LAE sample from spectral energy distribution (SED) fitting. These characteristics include mass, age, star-formation history, dust content, and metallicity. We also detail an approach to account for nebular emission lines in the SED fitting process - wherein our models predict the strength of the [O III] line in an LAE spectrum. We are able to study the success of this prediction because we can compare the model predictions to our actual near-infrared observations both in galaxies that have [O III] detections and those that yielded non-detections. We find a median stellar mass of 6.9 $\times$ 10$^8$ M$_{\odot}$ and a median star formation rate weighted stellar population age of 4.5 $\times$ 10$^6$ yr. In addition to SED fitting, we quantify the velocity offset between the [O III] and Ly$\alpha$ lines in the galaxy with the new [O III] detection, finding that the Ly$\alpha$ line is shifted 52 km s$^{-1}$ redwards of the [O III] line, which defines the systemic velocity of the galaxy.Comment: 38 pages, 27 figures, 4 tables, Accepted for publication in MNRA

Ly-alpha emitting galaxies at redshift z~4.5 in the LALA Cetus field

We present a large sample of Ly-alpha emitting galaxies spectroscopically confirmed at z~4.5, based on IMACS spectroscopic observations of candidate LAEs in the LALA Cetus field. We identify 110 z~4.5 LAEs based on single line detections with no continuum emission blueward of the line. The Ly-alpha confirmation rate varies from <50% to 76% for candidates selected in different narrowband filters at slightly different redshifts. We find a drop in the LAE density at redshift 4.50+-0.03 from redshift 4.39-4.47 by a factor of 66%, which could be a large scale void in the distribution of star-forming galaxies (~18Mpc along the line of sight and ~80Mpc across). The sample includes many objects with equivalent widths >200A. These large EW candidates are spectroscopically confirmed at the same rate as candidates with more modest EWs. A composite spectrum of all 110 confirmed LAEs shows the characteristic asymmetry of the Ly-alpha line. It also places new and stringent upper limits on the CIV 1549/Ly-alpha and HeII 1640/Ly-alpha line ratios, providing a new upper limit on the fraction of active galactic nuclei in Ly-alpha selected galaxy samples, and on the contribution of Pop III populations. Finally, we calculate the Ly-alpha luminosity function for our z~4.5 sample, which is consistent with those at other redshifts, showing that there is no evolution in Ly-alpha luminosity function from z~3.1-6.6.Comment: 30 pages, 10 figures, ApJ submitte

The Dynamical Masses, Densities, and Star Formation Scaling Relations of Lyman Alpha Galaxies

We present the first dynamical mass measurements for Lyman alpha galaxies at high redshift, based on velocity dispersion measurements from rest-frame optical emission lines and size measurements from HST imaging, for a sample of nine galaxies drawn from four surveys. These measurements enable us to study the nature of Lyman alpha galaxies in the context of galaxy scaling relations. The resulting dynamical masses range from 1e9 to 1e10 solar masses. We also fit stellar population models to our sample, and use them to plot the Lyman alpha sample on a stellar mass vs. line width relation. Overall, the Lyman alpha galaxies follow well the scaling relation established by observing star forming galaxies at lower redshift (and without regard for Lyman alpha emission), though in 1/3 of the Lyman alpha galaxies, lower-mass fits are also acceptable. In all cases, the dynamical masses agree with established stellarmass-linewidth relation. Using the dynamical masses as an upper limit on gas mass, we show that Lyman alpha galaxies resemble starbursts (rather than "normal" galaxies) in the relation between gas mass surface density and star formation activity, in spite of relatively modest star formation rates. Finally, we examine the mass densities of these galaxies, and show that their future evolution likely requires dissipational ("wet") merging. In short, we find that Lyman alpha galaxies are low mass cousins of larger starbursts.Comment: Submitted to The Astrophysical Journal. 23 pp including three figures and four table

Effects of Dust Geometry in Lyman Alpha Galaxies at z = 4.4

Equivalent widths (EWs) observed in high-redshift Lyman alpha galaxies could be stronger than the EW intrinsic to the stellar population if dust is present residing in clumps in the inter-stellar medium (ISM). In this scenario, continuum photons could be extinguished while the Lyman alpha photons would be resonantly scattered by the clumps, eventually escaping the galaxy. We investigate this radiative transfer scenario with a new sample of six Lyman alpha galaxy candidates in the GOODS CDF-S, selected at z = 4.4 with ground-based narrow-band imaging obtained at CTIO. Grism spectra from the HST PEARS survey confirm that three objects are at z = 4.4, and that another object contains an active galactic nuclei (AGN). If we assume the other five (non-AGN) objects are at z = 4.4, they have rest-frame EWs from 47 -- 190 A. We present results of stellar population studies of these objects, constraining their rest-frame UV with HST and their rest-frame optical with Spitzer. Out of the four objects which we analyzed, three objects were best-fit to contain stellar populations with ages on the order of 1 Myr and stellar masses from 3 - 10 x 10^8 solar masses, with dust in the amount of A_1200 = 0.9 - 1.8 residing in a quasi-homogeneous distribution. However, one object (with a rest EW ~ 150 A) was best fit by an 800 Myr, 6.6 x 10^9 solar mass stellar population with a smaller amount of dust (A_1200 = 0.4) attenuating the continuum only. In this object, the EW was enhanced ~ 50% due to this dust. This suggests that large EW Lyman alpha galaxies are a diverse population. Preferential extinction of the continuum in a clumpy ISM deserves further investigation as a possible cause of the overabundance of large-EW objects that have been seen in narrow-band surveys in recent years.Comment: Submitted to the Astrophysical Journal. 35 pages, 7 figures and 4 table

The Luminosity Function of Lyman alpha Emitters at Redshift z=7.7

Lyman alpha (Lya) emission lines should be attenuated in a neutral intergalactic medium (IGM). Therefore the visibility of Lya emitters at high redshifts can serve as a valuable probe of reionization at about the 50% level. We present an imaging search for z=7.7 Lya emitting galaxies using an ultra-narrowband filter (filter width= 9A) on the NEWFIRM imager at the Kitt Peak National Observatory. We found four candidate Lya emitters in a survey volume of 1.4 x 10^4 Mpc^3, with a line flux brighter than 6x10^-18 erg/cm^2/s (5 sigma in 2" aperture). We also performed a detailed Monte-Carlo simulation incorporating the instrumental effects to estimate the expected number of Lya emitters in our survey, and found that we should expect to detect one Lya emitter, assuming a non-evolving Lya luminosity function (LF) between z=6.5 and z=7.7. Even if one of the present candidates is spectroscopically confirmed as a z~8 Lya emitter, it would indicate that there is no significant evolution of the Lya LF from z=3.1 to z~8. While firm conclusions would need both spectroscopic confirmations and larger surveys to boost the number counts of galaxies, we successfully demonstrate the feasibility of sensitive near-infrared (1.06 um) narrow-band searches using custom filters designed to avoid the OH emission lines that make up most of the sky background.Comment: Published in ApJ, 3 figure