Natascha M. Förster-Schreiber

Shocked Superwinds from the z ~ 2 Clumpy Star-forming Galaxy, ZC406690

We have obtained high-resolution data of the z � 2 ring-like, clumpy star-forming galaxy (SFG) ZC406690 using the VLT/SINFONI with AO (in K-band) and in seeing-limited mode (in H- and J-band). Our data includes all of the main strong optical emission lines: [OII], [OIII], Hα, Hβ, [NII], and [SII]. We find broad, blueshifted Hα and [OIII] emission line wings in the spectra of the galaxy’s massive, star-forming clumps (σ � 85 km s −1 ) and even broader wings (up to 70% of the total Hα flux, with σ � 290 km s −1 ) in regions spatially offset from the clumps by � 2 kpc. The broad emission likely originates from large-scale outflows with mass outflow rates from individual clumps that are 1–8x the SFR of the clumps. Based on emission line ratio diagnostics ([NII]/Hα and [SII]/Hα) and photoionization and shock models, we find that the emission from the clumps is due to a combination of photoionization from the star-forming regions and shocks generated in the outflowing component, with 5–30% of the emission deriving from shocks. In terms of the ionization parameter (6x10 7 -10 8 cm/s, based on both the SFR and the O32 ratio), density (local electron densities of 300–1800 cm −3 in and around the clumps, and ionized gas column densities of 1200–8000 M⊙/pc 2 ), and SFR (10–40 M⊙ yr −1 ), these clumps more closely resemble nuclear starburst regions of local ULIRGs and dwarf irregulars than HII regions in local galaxies. However, the star-forming clumps are not located in the nucleus as in local starburst galaxies but instead are situated in a ring several kpc from the center of their high-redshift host galaxy, and have an overall disk-like morphology. The two brightest clumps are quite different in terms of their internal properties, energetics and relative ages, and thus we are given a glimpse at two different stages in the formation and evolution of rapidly star-forming giant clumps at high-z. Subject headings: galaxies: high redshift – galaxies: evolution – galaxies: emission lines – galaxies: star formation – ISM: jets and outflows

The mean star-forming properties of QSO host galaxies

Quasi-stellar objects (QSOs) occur in galaxies in which supermassive black holes (SMBHs) are growing substantially through rapid accretion of gas. Many popular models of the co-evolutionary growth of galaxies and black holes predict that QSOs are also sites of substantial recent star formation (SF), mediated by important processes, such as major mergers, which rapidly transform the nature of galaxies. A detailed study of the star-forming properties of QSOs is a critical test of these models. We present a far-infrared Herschel/PACS study of the mean star formation rate (SFR) of a sample of spectroscopically observed QSOs to z ∼ 2 from the COSMOS extragalactic survey. This is the largest sample to date of moderately luminous QSOs (with nuclear luminosities that lie around the knee of the luminosity function) studied using uniform, deep far-infrared photometry. We study trends of the mean SFR with redshift, black hole mass, nuclear bolometric luminosity, and specific accretion rate (Eddington ratio). To minimize systematics, we have undertaken a uniform determination of SMBH properties, as well as an analysis of important selection effects of spectroscopic QSO samples that influence the interpretation of SFR trends. We find that the mean SFRs of these QSOs are consistent with those of normal massive star-forming galaxies with a fixed scaling between SMBH and galaxy mass at all redshifts. No strong enhancement in SFR is found even among the most rapidly accreting systems, at odds with several co-evolutionary models. Finally, we consider the qualitative effects on mean SFR trends from different assumptions about the SF properties of QSO hosts and from redshift evolution of the SMBH-galaxy relationship. While currently limited by uncertainties, valuable constraints on AGN-galaxy co-evolution can emerge from our approach.

The effect of metal enrichment and galactic winds on galaxy formation in cosmological zoom simulations

We investigate the differential effects of metal cooling and galactic stellar winds on the cosmological formation of individual galaxies with three sets of cosmological, hydrodynamical zoom simulations of 45 halos in the mass range 10^11 1 and predict reasonable star formation histories, (ii) produce galaxies with high cold gas fractions (30-60 per cent) at high redshift, (iii) significantly reduce the galaxy formation efficiencies for halos (M_halo<10^12M_sun) at all redshifts in agreement with observational and abundance matching constraints, (iv) result in high-redshift galaxies with reduced circular velocities matching the observed Tully-Fisher relation at z~2, and (v) significantly increase the sizes of low-mass galaxies (M_stellar<3x10^10M_sun) at high redshift resulting in a weak size evolution - a trend in agreement with observations. However, the low redshift (z<0.5) star formation rates of massive galaxies are higher than observed (up to ten times). No tested model predicts the observed size evolution for low-mass and high-mass galaxies simultaneously. Due to the delayed onset of star formation in the wind models, the metal enrichment of gas and stars is delayed and agrees well with observational constraints. Metal cooling and stellar winds are both found to increase the ratio of in situ formed to accreted stars - the relative importance of dissipative vs. dissipationless assembly. For halo masses below ~10^12M_sun, this is mainly caused by less stellar accretion and compares well to predictions from semi-analytical models but still differs from abundance matching models. For higher masses, the fraction of in situ stars is over-predicted due to the unrealistically high star formation rates at low redshifts.

The Nature of Extreme Emission Line Galaxies at z=1-2: Kinematics and Metallicities from Near-Infrared Spectroscopy

We present near-infrared spectroscopy of a sample of 22 Extreme Emission Line Galaxies at redshifts 1.3 < z < 2.3, confirming that these are low-mass (M* = 108-109M(circle dot)) galaxies undergoing intense starburst episodes (M*/SFR similar to 10-100 Myr). The sample is selected by [O iii] or Ha emission line flux and equivalent width using near-infrared grism spectroscopy from the 3D-HST survey. High-resolution NIR spectroscopy is obtained with LBT/LUCI and VLT/X-SHOOTER. The [Oiii]/H line ratio is high (greater than or similar to 5) and [N ii]/Ha is always significantly below unity, which suggests a low gas-phase metallicity. We are able to determine gas-phase metallicities for seven of our objects using various strong-line methods, with values in the range 0.05-0.30 Z similar to and with a median of 0.15 Z similar to; for three of these objects we detect [O iii].4363, which allows for a direct constraint on the metallicity. The velocity dispersion, as measured from the nebular emission lines, is typically similar to 50 km s-1. Combined with the observed star-forming activity, the Jeans and Toomre stability criteria imply that the gas fraction must be large (fgas - 2/3), consistent with the difference between our dynamical and stellar mass estimates. The implied gas depletion timescale (several hundred Myr) is substantially longer than the inferred mass-weighted ages (similar to 50 Myr), which further supports the emerging picture that most stars in low-mass galaxies form in short, intense bursts of star formation.

Measures of galaxy dust and gas mass with Herschel photometry and prospects for ALMA

(Abridged) Combining the deepest Herschel extragalactic surveys (PEP, GOODS-H, HerMES), and Monte Carlo mock catalogs, we explore the robustness of dust mass estimates based on modeling of broad band spectral energy distributions (SEDs) with two popular approaches: Draine & Li (2007, DL07) and a modified black body (MBB). As long as the observed SED extends to at least 160-200 micron in the rest frame, M(dust) can be recovered with a >3 sigma significance and without the occurrence of systematics. An average offset of a factor ~1.5 exists between DL07- and MBB-based dust masses, based on consistent dust properties. At the depth of the deepest Herschel surveys (in the GOODS-S field) it is possible to retrieve dust masses with a S/N>=3 for galaxies on the main sequence of star formation (MS) down to M(stars)~1e10 [M(sun)] up to z~1. At higher redshift (z 1, the delta(GDR) dependence on metallicity is consistent with the local relation. We combine far-IR Herschel data and sub-mm ALMA expected fluxes to study the advantages of a full SED coverage.

Predicting Quiescence: The Dependence of Specific Star Formation Rate on Galaxy Size and Central Density at 0.5 < z < 2.5

NASA through Hubble Fellowship - Space Telescope Science Institute [HST-HF2-51368]; NASA [NAS 5-26555, NAS5-26555]; 3D-HST Treasury Program [GO 12177, 12328]; NASA/ ESA HST

Status of the KMOS multi-object near-infrared integral field spectrograph

KMOS is a multi-object near-infrared integral field spectrograph being built by a consortium of UK and German institutes. We report on the final integration and test phases of KMOS, and its performance verification, prior to commissioning on the ESO VLT later this year.

Ultradeep near-infrared imaging of HDF-South : rest frame optical properties of high redshift galaxies

We have obtained ultradeep Js, H and Ks near-infrared imaging of the Hubble Deep Field South WFPC2 field with the ISAAC camera on the VLT. The total integration time of 100 hours resulted in the deepest ground-based infrared observations to date and the deepest Ks-band data ever taken. This depth allows us to determine the spectral energy distributions of the high-redshift galaxies with unprecendented accuracy. Together with existing optical observations, we use the multicolor data to select high-redshift galaxies by their rest-frame optical light, and study their statistical properties and morphologies. We find a wide variety of morphologies: some are large in the rest-frame optical and resemble normal spiral galaxies, others are barely detected in the observers optical and have red NIR colors. The latter belong to a new population of galaxies at redshifts z>2, that is notably absent in the HDF-North. The spectral energy distributions of many of such red galaxies show distinct breaks, which we identify as the balmer break/4000 Angstrom break, and their contribution to the stellar mass density is estimated to be substantial. At redshift z~3, we find a clear excess of superluminious galaxies (> 5 L*B(z=0)), which is consistent with 1 magnitude of luminosity evolution. Overall, the results show the necessity of deep near-infrared imaging to obtain a full census of the high redshift universe.