We describe the search for Lyman-break galaxies (LBGs) near the sub-millimeter bright starburst galaxy HFLS3 at $z$$=$6.34 and a study on the environment of this massive galaxy during the end of reionization.We performed two independent selections of
LBGs on images obtained with the textit{Gran Telescopio Canarias} (GTC) and the textit{Hubble Space Telescope} (HST) by combining non-detections in bands blueward of the Lyman-break and color selection. A total of 10 objects fulfilling the LBG selection criteria at $z$$>$5.5 were selected over the 4.54 and 55.5 arcmin$^2$ covered by our HST and GTC images, respectively. The photometric redshift, UV luminosity, and the star-formation rate of these sources were estimated with models of their spectral energy distribution. These $z$$sim$6 candidates have physical properties and number densities in agreement with previous results. The UV luminosity function at $z$$sim$6 and a Voronoi tessellation analysis of this field shows no strong evidence for an overdensity of relatively bright objects (m$_{F105W}$$<$25.9) associated with textit{HFLS3}. However, the over-density parameter deduced from this field and the surface density of objects can not excluded definitively the LBG over-density hypothesis. Moreover we identified three faint objects at less than three arcseconds from textit{HFLS3} with color consistent with those expected for $z$$sim$6 galaxies. Deeper data are needed to confirm their redshifts and to study their association with textit{HFLS3} and the galaxy merger that may be responsible for the massive starburst.
Strong gravitational lenses are now being routinely discovered in wide-field surveys at (sub)millimeter wavelengths. We present Submillimeter Array (SMA) high-spatial resolution imaging and Gemini-South and Multiple Mirror Telescope optical spectrosc
opy of strong lens candidates discovered in the two widest extragalactic surveys conducted by the Herschel Space Observatory: the Herschel-Astrophysical Terahertz Large Area Survey (H-ATLAS) and the Herschel Multi-tiered Extragalactic Survey (HerMES). From a sample of 30 Herschel sources with S_500>100 mJy, 21 are strongly lensed (multiply imaged), 4 are moderately lensed (singly imaged), and the remainder require additional data to determine their lensing status. We apply a visibility-plane lens modeling technique to the SMA data to recover information about the masses of the lenses as well as the intrinsic (i.e., unlensed) sizes (r_half) and far-infrared luminosities (L_FIR) of the lensed submillimeter galaxies (SMGs). The sample of lenses comprises primarily isolated massive galaxies, but includes some groups and clusters as well. Several of the lenses are located at z_lens>0.7, a redshift regime that is inaccessible to lens searches based on Sloan Digital Sky Survey spectroscopy. The lensed SMGs are amplified by factors that are significantly below statistical model predictions given the 500um flux densities of our sample. We speculate that this may reflect a deficiency in our understanding of the intrinsic sizes and luminosities of the brightest SMGs. The lensed SMGs span nearly one decade in L_FIR (median L_FIR=7.9x10^12 L_sun) and two decades in FIR luminosity surface density (median Sigma_FIR=6.0x10^11 L_sun kpc^-2). The strong lenses in this sample and others identified via (sub-)mm surveys will provide a wealth of information regarding the astrophysics of galaxy formation and evolution over a wide range in redshift.
We have analysed the rest-frame far infrared (FIR) properties of a sample of massive (Mstar > 10^11Msun) galaxies at 2<z<3 in the GOODS (Great Observatories Origins Deep Survey) North field using the Spectral and Photometric Imaging Receiver (SPIRE)
instrument aboard the Herschel Space Observatory. To conduct this analysis we take advantage of the data from the HerMES key program. The sample comprises 45 massive galaxies with structural parameters characterised with HST NICMOS-3. We study detections at submm Herschel bands, together with Spitzer 24{mu}m data, as a function of the morphological type, mass and size. We find that 26/45 sources are detected at MIPS-24{mu}m and 15/45 (all MIPS-24{mu}m detections) are detected at SPIRE-250{mu}m, with disk-like galaxies more easily detected. We derive star formation rates (SFR) and specific star formation rates (sSFR) by fitting the spectral energy distribution (SED) of our sources, taking into account non-detections for SPIRE and systematic effects for MIPS derived quantities. We find that the mean SFR for the spheroidal galaxies (50-100 Msun*yr^-1) is substantially (a factor ~ 3) lower than the mean value presented by disk-like galaxies (250-300 Msun*yr^-1).
We present results on low-resolution mid-infrared (MIR) spectra of 70 infrared-luminous galaxies obtained with the Infrared Spectrograph (IRS) onboard Spitzer. We selected sources from the European Large Area Infrared Survey (ELAIS) with S15 > 0.8 mJ
y and photometric or spectroscopic z > 1. About half of the sample are QSOs in the optical, while the remaining sources are galaxies, comprising both obscured AGN and starbursts. We classify the spectra using well-known infrared diagnostics, as well as a new one that we propose, into three types of source: those dominated by an unobscured AGN (QSOs), obscured AGN, and starburst-dominated sources. Starbursts concentrate at z ~ 0.6-1.0 favored by the shift of the 7.7-micron PAH band into the selection 15 micron band, while AGN spread over the 0.5 < z < 3.1 range. Star formation rates (SFR) are estimated for individual sources from the luminosity of the PAH features. An estimate of the average PAH luminosity in QSOs and obscured AGN is obtained from the composite spectrum of all sources with reliable redshifts. The estimated mean SFR in the QSOs is 50-100 Mo yr^-1, but the implied FIR luminosity is 3-10 times lower than that obtained from stacking analysis of the FIR photometry, suggesting destruction of the PAH carriers by energetic photons from the AGN. The SFR estimated in obscured AGN is 2-3 times higher than in QSOs of similar MIR luminosity. This discrepancy might not be due to luminosity effects or selection bias alone, but could instead indicate a connection between obscuration and star formation. However, the observed correlation between silicate absorption and the slope of the near- to mid-infrared spectrum is compatible with the obscuration of the AGN emission in these sources being produced in a dust torus.
