No abstract

Spectroscopic observations of Hα and Hβ emission lines of 128 star-forming galaxies in the redshift range 0.75 ≤ z ≤ 1.5 are presented. These data were taken with slitless spectroscopy using the G102 and G141 grisms of the Wide-Field-Camera 3 (WFC3) on board the Hubble Space Telescope as part of the WFC3 Infrared Spectroscopic Parallel (WISP) survey. Interstellar dust extinction is measured from stacked spectra that cover the Balmer decrement (Hα/Hβ). We present dust extinction as a function of Hα luminosity (down to 3 × 10 41 erg s −1 ), galaxy stellar mass (reaching 4 × 10 8 M ), and rest-frame Hα equivalent width. The faintest galaxies are two times fainter in Hα luminosity than galaxies previously studied at z ∼ 1.5. An evolution is observed where galaxies of the same Hα luminosity have lower extinction at higher redshifts, whereas no evolution is found within our error bars with stellar mass. The lower Hα luminosity galaxies in our sample are found to be consistent with no dust extinction. We find an anti-correlation of the [O III]λ5007/Hα flux ratio as a function of luminosity where galaxies with L Hα < 5 × 10 41 erg s −1 are brighter in [O III]λ5007 than Hα. This trend is evident even after extinction correction, suggesting that the increased [O III]λ5007/Hα ratio in low luminosity galaxies is likely due to lower metallicity and/or higher ionization parameters.

We report the discovery of a group of galaxies at redshift 2.38. We imaged about 10% of a claimed supercluster of QSO absorption-lines at z=2.38 (Francis & Hewett 1993). In this small field (2 arcmin radius) we detect two Ly-alpha emitting galaxies. The discovery of two such galaxies in our tiny field supports Francis & Hewett's interpretation of the absorption-line supercluster as a high redshift "Great Wall". One of the Ly-alpha galaxies lies 22 arcsec from a background QSO, and may be associated with a multi-component Ly-alpha absorption complex seen in the QSO spectrum. This galaxy has an extended (50kpc) lumpy Ly-alpha morphology, surrounding a compact IR-bright nucleus. The nucleus shows a pronounced break in its optical-UV colors at about 4000 A (rest-frame), consistent with a stellar population of mass about 7E11 solar masses, an age of more than 500 Myr, and little on-going star-formation. C IV emission is detected, suggesting that a concealed AGN is present. Extended H-alpha emission is also detected; the ratio of Ly-alpha flux to H-alpha is abnormally low (about 0.7), probable evidence for extended dust. This galaxy is surrounded by a number of very red (B-K>5) objects, some of which have colors suggesting that they too are at z=2.38. We hypothesize that this galaxy, its neighbors and a surrounding lumpy gas cloud may be a giant elliptical galaxy in the act of bottom-up formation.Comment: Accepted for publication in ApJ (Feb 1st 1996 issue). 23 pages, uuencoded compressed tar postscript figures (1.4 Mbytes). Text and figures also available from http://www.ph.unimelb.edu.au/~pjf/blob.html in ps forma

We analyse the velocity dispersion properties of 472 z ∼ 0.9 star-forming galaxies observed as part of the KMOS Redshift One Spectroscopic Survey (KROSS). The majority of this sample is rotationally dominated (83 ± 5% with v C /σ 0 > 1) but also dynamically hot and highly turbulent. After correcting for beam smearing effects, the median intrinsic velocity dispersion for the final sample is σ 0 = 43.2 ± 0.8 km s −1 with a rotational velocity to dispersion ratio of v C /σ 0 = 2.6 ± 0.1. To explore the relationship between velocity dispersion, stellar mass, star formation rate and redshift we combine KROSS with data from the SAMI survey (z ∼ 0.05) and an intermediate redshift MUSE sample (z ∼ 0.5). While there is, at most, a weak trend between velocity dispersion and stellar mass, at fixed mass there is a strong increase with redshift. At all redshifts, galaxies appear to follow the same weak trend of increasing velocity dispersion with star formation rate. Our results are consistent with an evolution of galaxy dynamics driven by disks that are more gas rich, and increasingly gravitationally unstable, as a function of increasing redshift. Finally, we test two analytic models that predict turbulence is driven by either gravitational instabilities or stellar feedback. Both provide an adequate description of the data, and further observations are required to rule out either model.