S. Arribas

Kinemetry of SINS high-redshift star-forming galaxies: distinguishing rotating disks from major mergers

We present a simple set of kinematic criteria that can distinguish between galaxies dominated by ordered rotational motion and those involved in major merger events. Our criteria are based on the dynamics of the warm ionized gas (as traced by Hα) within galaxies, making this analysis accessible to high-redshift systems, whose kinematics are primarily traceable through emission features. Using the method of kinemetry (developed by Krajnovic and coworkers), we quantify asymmetries in both the velocity and velocity dispersion maps of the warm gas, and the resulting criteria enable us to empirically differentiate between nonmerging and merging systems at high redshift. We apply these criteria to 11 of our best-studied rest-frame UV/optical-selected z ~ 2 galaxies for which we have near-infrared integral-field spectroscopic data from SINFONI on the VLT. Of these 11 systems, we find that >50% have kinematics consistent with a single rotating disk interpretation, while the remaining systems are more likely undergoing major mergers. This result, combined with the short formation timescales of these systems, provides evidence that rapid, smooth accretion of gas plays a significant role in galaxy formation at high redshift.

Erratum The effective temperature scale of giant stars (F0-K5) - II. Empirical calibration of

The sign of coefficient

T_{\mathsf {eff}}

a(3)

versus colours and [Fe/H]

in the general formula of Table 2 should be plus instead of minus. Thus, the formula should read:

Detection of the 2175 Å Extinction Feature at z = 0.83

\theta_{\rm eff}=a_{0} + a_{1} X + a_{2} X^{2} + a_{3} X {\rm [Fe/H]} + a_{4} {\rm [Fe/H]} + a_{5} {\rm [Fe/H]}^{2}.

VLT-VIMOS integral field spectroscopy of luminous and ultraluminous infrared galaxies - II. Evidence for shock ionization caused by tidal forces in the extra-nuclear regions of interacting and merging LIRGs

The observational study of star formation relations in gala xies is central to unraveling the related physical processe s that are at work on both local and global scales. It is still debated whether s tar formation can be described by a universal law that remains valid in different populations of galaxies. We wish to expand the sample of extreme starbursts, represented by local luminous and ultraluminous infrared galaxies (LIRGs and ULIRGs), with high quality observations in the 1‐0 line of HCN, which is taken as a proxy for the dense molecular gas content. The new data presented in this work allow us to enlarge in particular the number of LIRGs studied in HCN by a factor 3 compared to previous works. The chosen LIRG sample has a range of HCN luminosities that partly overlaps with that of the normal galaxy population. We study if a universal law can account for the star formation relations observed for the dense molecular gas in normal star forming galaxies and extreme starbursts and explore the validity of different theoretical prescriptions of the star formation law. We have used the IRAM 30m telescope to observe a sample of 19 LIRGs in the 1‐0 lines of CO, HCN and HCO + . The galaxies have been extracted from a sample of local LIRGs with available high-quality and high-resolution images obtained at optical, near and mid IR wavelengths, which probe the star formation activity. We have thus derived the star f ormation rates using different tracers and determined the sizes of the star forming regions in all the targets. The analysis of the new data proves that the effi ciency of star formation in the dense molecular gas (SFEdense) of extreme starbursts is a factor 3‐4 higher compared to normal galaxies. Kennicutt-Schmidt (KS) power laws have also been derived. We find a dua lity in KS laws that is further reinforced if we account for the likel y different conversion factor for HCN (α HCN ) in extreme starbursts and for the unobscured star formation rate in normal galaxies. This result extends to the higher molecular densities probed by HCN lines the more extreme bimodal behavior of star formation laws, derived from CO molecular lines by two recent surveys. We have confronted our observations with the predictions of theoretical models in which the effi ciency of star formation is determined by the ratio of a constant star formation rate per free-fall time (SFRff) to the local free-fall time (tff). We find that it is possible to fit the observed differences in the SFEdense between normal galaxies and LIRGs/ULIRGs using a common constant SFRff and a set of physically acceptable HCN densities, but only if SFRff∼0.005‐0.01 and/or ifα HCN is a factor of∼a few lower than our favored values. Star formation recipes that explicitly depend on the galaxy global dynamical time scales do not significantly improve th e fit to the new HCN data presented in this work.

Chandra Observations of Extended X-Ray Emission in ARP 220

We determine the extinction curve in the z_l=0.83 lens galaxy of the gravitational lens SBS0909+532 from the wavelength dependence of the flux ratio between the lensed quasar images (z_s=1.38) from 3400 to 9200\AA. It is the first measurement of an extinction curve at a cosmological distance of comparable quality to those obtained within the Galaxy. The extinction curve has a strong 2175\AA feature, a noteworthy fact because it has been weak or non-existent in most estimates of extinction curves outside the Galaxy. The extinction curve is fitted well by a standard