Starburst Intensity Limit of Galaxies at z~5-6

The peak star formation intensity in starburst galaxies does not vary significantly from the local universe to redshift z~6. We arrive at this conclusion through new surface brightness measurements of 47 starburst galaxies at z~5-6, doubling the redshift range for such observations. These galaxies are spectroscopically confirmed in the Hubble Ultra Deep Field (HUDF) through the GRism ACS program for Extragalactic Science (GRAPES) project. The starburst intensity limit for galaxies at z~5-6 agree with those at z~3-4 and z~0 to within a factor of a few, after correcting for cosmological surface brightness dimming and for dust. The most natural interpretation of this constancy over cosmic time is that the same physical mechanisms limit starburst intensity at all redshifts up to z~6 (be they galactic winds, gravitational instability, or something else). We do see two trends with redshift: First, the UV spectral slope of galaxies at z~5-6 is bluer than that of z~3 galaxies, suggesting an increase in dust content over time. Second, the galaxy sizes from z~3 to z~6 scale approximately as the Hubble parameter 1/H(z). Thus, galaxies at z~6 are high redshift starbursts, much like their local analogs except for slightly bluer colors, smaller physical sizes, and correspondingly lower overall luminosities. If we now assume a constant maximum star formation intensity, the differences in observed surface brightness between z~0 and z~6 are consistent with standard expanding cosmology and strongly inconsistent with tired light model.Comment: Accepted for publication in ApJ (23 pages, 5 figures). Minor changes to tex

The VIMOS Ultra Deep Survey: Lyα emission and stellar populations of star-forming galaxies at 2 < z < 2.5

The aim of this paper is to investigate spectral and photometric properties of 854 faint (i_(AB) ≲ 25 mag) star-forming galaxies (SFGs) at 2  0 Å), and Lyα emitters (LAEs; EW ≥ 20 Å). The fraction of LAEs at these redshifts is ~10%, which is consistent with previous observations. We compared best-fitSED-estimated stellar parameters of the SFG_N, SFG_L and LAE samples. For the luminosities probed here (~ L^∗), we find that galaxies with and without Lyα in emission have small but significant differences in their SED-based properties. We find that LAEs have less dust, and lower star-formation rates (SFR) compared to non-LAEs. We also find that LAEs are less massive compared to non-LAEs, though the difference is smaller and less significant compared to the SFR and Es(B−V). When we divide the LAEs according to their Spitzer/IRAC 3.6 μm fluxes, we find that the fraction of IRAC-detected (m_(3.6) ≲ 25 mag) LAEs is much higher than the fraction of IRAC-detected narrow band (NB)-selected LAEs at z ≃ 2–3. This could imply that UV-selected LAEs host a more evolved stellar population, which represents a later stage of galaxy evolution, compared to NB-selected LAEs

Near-Infrared Survey of the GOODS-North Field: Search for Luminous Galaxy Candidates at z=>6.5

We present near-infrared (NIR; J & Ks) survey of the Great Observatories Origins Deep Survey-North (GOODS-N) field. The publicly available imaging data were obtained using the MOIRCS instrument on the 8.2m Subaru and the WIRCam instrument on the 3.6m Canada-France-Hawaii Telescope (CFHT). These observations fulfill a serious wavelength gap in the GOODS-N data - i.e., lack of deep NIR observations. We combine the Subaru/MOIRCS and CFHT/WIRCam archival data to generate deep J and Ks band images, covering the full GOODS-N field (~169 sq. arcmin) to an AB magnitude limit of ~25 mag (3sigma). We applied z'-band dropout color selection criteria, using the NIR data generated here. We have identified two possible Lyman Break Galaxy (LBG) candidates at z\gtrsim6.5 with J\lesssim24.5. The first candidate is a likely LBG at z\sim6.5 based on a weak spectral feature tentatively identified as Lyalpha line in the deep Keck/DEIMOS spectrum, while the second candidate is a possible LBG at z\sim7 based on its photometric redshift. These z'-dropout objects, if confirmed, are among the brightest such candidates found so far. At z\gtrsim6.5, their star formation rate is estimated as 100-200 solar mass per year. If they continue to form stars at this rate, they assemble a stellar mass of ~5x10^10 solar mass after about 400 million years, becoming the progenitors of massive galaxies observed at z\sim5. We study the implication of the z'-band dropout candidates discovered here, in constraining the bright-end of the luminosity function and understanding the nature of high redshift galaxies.Comment: ApJ in press, minor text/reference update

Martian atmospheric O₃ retrieval development for the NOMAD-UVIS spectrometer

The composition of atmospheric trace gases and aerosols is a highly variable and poorly constrained component of the martian atmosphere, and by affecting martian climate and UV surface dose, represents a key parameter in the assessment of suitability for martian habitability. The ExoMars Trace Gas Orbiter (TGO) carries the Open University (OU) designed Ultraviolet and VIsible Spectrometer (UVIS) instrument as part of the Belgian-led Nadir and Occultation for MArs Discovery (NOMAD) spectrometer suite. NOMAD will begin transmitting science observations of martian surface and atmosphere back-scattered UltraViolet (UV) and visible radiation in Spring 2018, which will be processed to derive spatially and temporally averaged atmospheric trace gas and aerosol concentrations, intended to provide a better understanding of martian atmospheric photo-chemistry and dynamics, and will also improve models of martian atmospheric chemistry, climate and habitability. Work presented here illustrates initial development and testing of the OU’s new retrieval algorithm for determining O3 and aerosol concentrations from the UVIS instrument

"GiGa": the Billion Galaxy HI Survey -- Tracing Galaxy Assembly from Reionization to the Present

In this paper, we review the Billion Galaxy Survey that will be carried out at radio--optical wavelengths to micro--nanoJansky levels with the telescopes of the next decades. These are the Low-Frequency Array, the Square Kilometer Array and the Large Synoptic Survey Telescope as survey telescopes, and the Thirty Meter class Telescopes for high spectral resolution+AO, and the James Webb Space Telescope (JWST) for high spatial resolution near--mid IR follow-up. With these facilities, we will be addressing fundamental questions like how galaxies assemble with super-massive black-holes inside from the epoch of First Light until the present, how these objects started and finished the reionization of the universe, and how the processes of star-formation, stellar evolution, and metal enrichment of the IGM proceeded over cosmic time. We also summarize the high-resolution science that has been done thus far on high redshift galaxies with the Hubble Space Telescope (HST). Faint galaxies have steadily decreasing sizes at fainter fluxes and higher redshifts, reflecting the hierarchical formation of galaxies over cosmic time. HST has imaged this process in great structural detail to z<~6. We show that ultradeep radio-optical surveys may slowly approach the natural confusion limit, where objects start to unavoidably overlap because of their own sizes, which only SKA can remedy with HI redshifts for individual sub-clumps. Finally, we summarize how the 6.5 meter James Webb Space Telescope (JWST) will measure first light, reionization, and galaxy assembly in the near--mid-IR.Comment: 8 pages, LaTeX2e requires 'aip' style (included), 8 postscript figures. To appear in the proceedings of the `The Evolution of Galaxies through the Neutral Hydrogen Window' conference, Arecibo Observatory Feb 1-3, 2008; Eds. R. Minchin & E. Momjian, AIP Conf Pro

Surface Brightness Profiles of Composite Images of Compact Galaxies at z~4-6 in the HUDF

The Hubble Ultra Deep Field (HUDF) contains a significant number of B, V and i'-band dropout objects, many of which were recently confirmed to be young star-forming galaxies at z~4-6. These galaxies are too faint individually to accurately measure their radial surface brightness profiles. Their average light profiles are potentially of great interest, since they may contain clues to the time since the onset of significant galaxy assembly. We separately co-add V, i' and z'-band HUDF images of sets of z~4,5 and 6 objects, pre-selected to have nearly identical compact sizes and the roundest shapes. From these stacked images, we are able to study the averaged radial structure of these objects at much higher signal-to-noise ratio than possible for an individual faint object. Here we explore the reliability and usefulness of a stacking technique of compact objects at z~4-6 in the HUDF. Our results are: (1) image stacking provides reliable and reproducible average surface brightness profiles; (2) the shape of the average surface brightness profiles show that even the faintest z~4-6 objects are resolved; and (3) if late-type galaxies dominate the population of galaxies at z~4-6, as previous HST studies have shown, then limits to dynamical age estimates for these galaxies from their profile shapes are comparable with the SED ages obtained from the broadband colors. We also present accurate measurements of the sky-background in the HUDF and its associated 1-sigma uncertainties.Comment: 10 pages, 9 figures, 2 tables, emulateapj; Accepted for publication in The Astronomical Journa