Galaxy formation and evolution

Abstract:

We present observations of early-type galaxies with laser guide star adaptive optics (LGS AO) obtained at Gemini North telescope using the NIFS integral field unit (IFU). We employ an innovative technique where the focus compensation due to the changing distance to the sodium layer is made 'open loop', allowing the extended galaxy nucleus to be used only for tip-tilt correction. The purpose of these observations is to determine high spatial resolution stellar kinematics within the nuclei of these galaxies to determine the masses of the super-massive black holes. The resulting data have spatial resolution of 0.2" FWHM or better. This is sufficient to positively constrain the presence of the central black hole in even low-mass early-type galaxies, suggesting that larger samples of such objects could be observed with this technique in the future. The open-loop focus correction technique is a supported queue-observing mode at Gemini, significantly extending the sky coverage in particular for faint, extended guide sources. We also provide preliminary results from tests combining tip/tilt correction from the Gemini peripheral guider with on-axis LGS. The current test system demonstrates feasibility of this mode, providing about a factor 2-3 improvement over natural seeing. With planned upgrades to the peripheral wave-front sensor, we hope to provide close to 100% sky coverage with low Strehl corrections, or 'improved seeing', significantly increasing flux concentration for deep field and extended object studies. © 2010 SPIE.

Abstract:

We present a derivation of the star formation rate per comoving volume of quasar host galaxies, derived from stacking analyses of far-infrared to mm-wave photometry of quasars with redshifts 0 < z < 6 and absolute I-band magnitudes -22 > IAB > -32 We use the science demonstration observations of the first ∼ 16 deg2 from the Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS) in which there are 240 quasars from the Sloan Digital Sky Survey (SDSS) and a further 171 from the 2dF-SDSS LRG and QSO (2SLAQ) survey. We supplement this data with a compilation of data from IRAS, ISO, Spitzer, SCUBA and MAMBO. H-ATLAS alone statistically detects the quasars in its survey area at > 5σ at 250, 350 and 500 μ m. From the compilation as a whole we find striking evidence of downsizing in quasar host galaxy formation: low-luminosity quasars with absolute magnitudes in the range -22 > IAB > -24 have a comoving star formation rate (derived from 100 μ m rest-frame luminosities) peaking between redshifts of 1 and 2, while high-luminosity quasars with IAB < -26 have a maximum contribution to the star formation density at z ∼ 3. The volume-averaged star formation rate of -22 > IAB > -24 quasars evolves as (1 + z)2.3±0.7 at z < 2, but the evolution at higher luminosities is much faster reaching (1 + z) 10±1 at -26 > IAB > -28. We tentatively interpret this as a combination of a declining major merger rate with time and gas consumption reducing fuel for both black hole accretion and star formation. © 2010 ESO.

Abstract:

We present a detailed analysis of the far-infrared (-IR) properties of the bright, lensed, z = 2.3, submillimetre-selected galaxy (SMG), SMM J2135-0102 (hereafter SMM J2135), using new observations with Herschel, SCUBA-2 and the Very Large Array (VLA). These data allow us to constrain the galaxy's spectral energy distribution (SED) and show that it has an intrinsic rest-frame 8-1000-μm luminosity, Lbol, of (2.3±0.2) × 10 12 L⊙ and a likely star-formation rate (SFR) of ∼400 M⊙ yr-1. The galaxy sits on the far-IR/radio correlation for far-IR-selected galaxies. At ≥70 μm, the SED can be described adequately by dust components with dust temperatures, Td ∼ 30 and 60 k. Using SPIRE's Fourier- transform spectrometer (FTS) we report a detection of the [C ii] 158 μm cooling line. If the [C ii], CO and far-IR continuum arise in photo-dissociation regions (PDRs), we derive a characteristic gas density, n ∼ 103 cm-3, and a far-ultraviolet (-UV) radiation field, G0, 103× stronger than the Milky Way. L[CII]/Lbol is significantly higher than in local ultra-luminous IR galaxies (ULIRGs) but similar to the values found in local star-forming galaxies and starburst nuclei. This is consistent with SMM J2135 being powered by starburst clumps distributed across ∼2 kpc, evidence that SMGs are not simply scaled-up ULIRGs. Our results show that SPIRE's FTS has the ability to measure the redshifts of distant, obscured galaxies via the blind detection of atomic cooling lines, but it will not be competitive with ground-based CO-line searches. It will, however, allow detailed study of the integrated properties of high-redshift galaxies, as well as the chemistry of their interstellar medium (ISM), once more suitably bright candidates have been found. © ESO 2010.

Abstract:

We present Herschel-PACS observations of rest-frame mid-infrared and far-infrared spectral line emissions from two lensed, ultraluminous infrared galaxies at high redshift: MIPS J142824.0+352619 (MIPS J1428), a starburst-dominated system at z = 1.3, and IRAS F10214+4724 (F10214), a source at z = 2.3 hosting both star-formation and a luminous AGN. We have detected [OI]63μm and [OIII]52μm in MIPS J1428, and tentatively [O III]52μm in F10214. Together with the recent ZEUS-CSO [CII]158μm detection in MIPS J1428 we can for the first time combine [OI], [CII] and far-IR (FIR) continuum measurements for PDR modeling of an ultra-luminous (LIR ≥ 10 12 L⊙) star forming galaxy at the peak epoch of cosmic star formation. We find that MIPS J1428, contrary to average local ULIRGs, does not show a deficit in [OI] relative to FIR. The combination of far-UV flux G0 and gas density n (derived from the PDR models), as well as the star formation efficiency (derived from CO and FIR) is similar to normal or starburst galaxies, despite the high infrared luminosity of this system. In contrast, F10214 has stringent upper limits on [O IV] and [S III], and an [O III]/FIR ratio at least an order of magnitude lower than local starbursts or AGN, similar to local ULIRGs. © ESO 2010.

Abstract:

We set out to determine the ratio, qIR, of rest-frame 8-1000-μm flux, SIR, to monochromatic radio flux, S 1.4 GHz, for galaxies selected at far-infrared (IR) and radio wavelengths, to search for signs that the ratio evolves with redshift, luminosity or dust temperature, Td, and to identify any far-IR-bright outliers - useful laboratories for exploring why the far-IR/radio correlation (FIRRC) is generally so tight when the prevailing theory suggests variations are almost inevitable. We use flux-limited 250-μm and 1.4-GHz samples, obtained using Herschel and the Very Large Array (VLA) in GOODS-North (-N). We determine bolometric IR output using ten bands spanning λobs = 24-1250 μm, exploiting data from PACS and SPIRE (PEP; HerMES), as well as Spitzer, SCUBA, AzTEC and MAMBO. We also explore the properties of an L IR-matched sample, designed to reveal evolution of qIR with redshift, spanning log LIR = 11-12 L⊙ and z = 0-2, by stacking into the radio and far-IR images. For 1.4-GHz-selected galaxies in GOODS-N, we see tentative evidence of a break in the flux ratio, q IR, at L1.4 GHz ∼ 1022.7 W Hz-1, where active galactic nuclei (AGN) are starting to dominate the radio power density, and of weaker correlations with redshift and Td. From our 250-μm-selected sample we identify a small number of far-IR-bright outliers, and see trends of qIR with L1.4 GHz, LIR, Td and redshift, noting that some of these are inter-related. For our LIR-matched sample, there is no evidence that qIR changes significantly as we move back into the epoch of galaxy formation: we find qIR (1+z)γ, where γ = -0.04±0.03 at z = 0-2; however, discounting the least reliable data at z < 0.5 we find γ = -0.26±0.07, modest evolution which may be related to the radio background seen by ARCADE 2, perhaps driven by <10-μJy radio activity amongst ordinary star-forming galaxies at z>1. © ESO 2010.