GRB host galaxies studies with X‐shooter

Gamma‐ray bursts (GRBs) are the most powerful explosions since the formation of the Universe, associated with the death of massive stars or mergers of compact stellar objects. Several recent striking results strongly support the idea that host galaxies of GRBs are opening a new view on our understanding of galaxy formation and evolution, back to the very primordial universe at z ∼ 8. They form a unique sample of galaxies which cover a wide range of redshift, they are typically weak with low mass and unlike other methods they are not selected on luminosity. In recent years, thanks to the support of new generation instruments, multi‐band photometry and spectroscopy allow us to better investigate the properties of these host galaxies (e.g., stellar mass, age, SFR, metallicity), to study their possible evolution and to compare them with field galaxies and other classes of galaxies. GRB host spectroscopy is one of the main science drivers behind the X‐shooter spectrograph. In this paper, we present the first results of the program devoted to Italian‐French GTO multiband spectroscopy of GRB host galaxies with X‐shooter (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Metallicities of high redshift GRB hosts: The case of GRB 100219A

GRB 100219A at z = 4.667 has been the highest redshift gamma‐ray burst observed with the X‐shooter spectrograph up to now. The spectrum covering the range from 5000 to 24000 Å and a large number of absorption lines allows to make a detailed study of the interstellar medium in a high redshift galaxy. The ISM in the low ionisation state and the kinematics of the absorption line components reveal a complex velocity field. The metallicity measured from different absorption lines is around 0.1 solar. Other GRB hosts at redshift beyond ∼3 have similar metallicities albeit with a large scatter in the metallicity distribution. X‐shooter will allow us to determine metallicities of a larger number of GRB hosts beyond redshift 5, to probe the early chemical enrichment of the Universe and to study its evolution from redshift 2 to beyond 10 (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Star‐forming galaxies observed with X‐shooter

In the last couple of decades hundreds of studies have explored the nature of star‐forming galaxies at different redshifts. This contribution focuses on X‐shooter observations of star‐burst galaxies at 0 < z < 6 from commissioning runs, science verification, and regular observations, and demonstrates the capability of the new instrument in this competitive field. Observations of gravitationally lensed galaxies show that X‐shooter has no limitation in the redshift desert (1.4 < z < 2) where the strong optical emission lines are shifted to the near‐IR region. Physical properties of galaxies, such as masses, metallicities, abundance ratios, and star formation rates can be derived from observations with relatively short integration times for faint galaxies. The simultaneous UV to near‐IR spectral coverage makes derivation of physical quantities more reliable because there are no differential slit losses as may occur when observations from different optical and near‐IR instruments are used. Over the entire redshift range, spectra of faint galaxies will allow us to better measure stellar ages and dominating ionisation sources compared to broad band spectral energy distribution measurements (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Time resolved spectroscopy of GRB 100418A and its host galaxy with X‐shooter

GRB 100418A was an intermediate duration GRB detected by Swift. It showed an initially dim optical afterglow that had a late increase in brightness, reaching its maximum several hours after the burst onset, unlike typical afterglows that peak tens of seconds after. It also displayed a bright X‐ray and radio counterpart. In this paper we present the observations of the afterglow obtained with X‐shooter. Three epochs were obtained, 0.4, 1.4, and 2.4 days after the burst. In these spectra, each covering the range from 3000 to 24800 Å, we detect abundant absorption features with 4 velocity components, and emission lines from the host galaxy with 2 additional velocity components. In one single velocity component, we detect a Fe II* 2396 Å fine structure feature which disappears from the first to the second epoch indicating that it is due to the effect of the GRB radiation on its environment. We consider it to be the closest absorption component to the GRB itself, for which we determine a redshift of z = 0.6239 ± 0.0002. From the Hα to [N II] ratio we determine a host galaxy metallicity of 0.5 solar (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Studying the diverse nature of faint galaxies in nearby clusters of the WINGS sample

We present the first results of our X‐shooter observations for a sample of dwarf (–17 < M_B < –15) galaxies in nearby (0.04 < z < 0.07) galaxy clusters. This luminosity range is fundamental to trace the evolution of higher‐z star‐forming cluster galaxies down to the present day, and to explore the galaxy scaling relations of early‐type galaxies over a broad mass range. Thanks to high resolution and availability of several lines we can derive the velocity dispersion of the galaxies in this range of luminosities and we begin the construction of the fundamental plane of faint early‐type galaxies (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Ly+ and ultraviolet emission from high-redshift gamma-ray burst hosts: to what extent do gamma-ray bursts trace star formation?

We report the result of a search for Lyα emission from the host galaxies of the gamma-ray bursts  (GRBs) 030226 ( z = 1.986), 021004 ( z = 2.335)  and  020124 ( z = 3.198)  . We find that the host galaxy of GRB 021004 is an extended (around 8 kpc) strong Lyα emitter with a rest-frame equivalent width (EW) of 68⁺¹²₋₁₁Å, and a star formation rate of  10.6 ± 2.0 M_⊙ yr⁻¹  . We do not detect the hosts of GRB 030226 and GRB 020124, but the upper limits on their Lyα fluxes do not rule out large rest-frame EWs. In the fields of GRB 021004 and GRB 030226 we find seven and five other galaxies, respectively, with excess emission in the narrow-band filter. These galaxies are candidate Lyα-emitting galaxies in the environment of the host galaxies. We have also compiled a list of all   z ≳ 2  GRB hosts, and demonstrate that a scenario where they trace star formation in an unbiased way is compatible with current observational constraints. Fitting the   z = 3  luminosity function (LF) under this assumption results in a characteristic luminosity of   R *= 24.6  and a faint-end slope of  α=−1.55  , consistent with the LF measured for Lyman-break galaxies.     

Using X‐shooter to measure the extinction in long GRB host galaxies from emission lines

The spectra of the host galaxies of gamma‐ray bursts at low redshift generally show strong hydrogen lines of the Balmer, Paschen and Brackett series, in addition to strong nebular metal lines. In special cases the hosts can be resolved in separate star forming regions, and spatially resolved spectroscopy can be obtained. Generally, the three strongest Balmer lines are used to derive the reddening experienced by the emission lines of the host gas, assuming a Milky Way extinction curve, case B recombination and a fixed electron temperature. We demonstrate how the wide wavelength range of X‐shooter, in combination with a rigorous calibration strategy, can be used to fit explicitly for R_V, T_e, and A_V simultaneously using a large number of H and He I recombination lines, explicitly corrected for stellar atmosphere absorption. This increases our understanding of extinction and absorption in starforming regions in GRB hosts. We use two GRB hosts as examples of the methods, outlining the advantages of using X‐shooter over other instruments (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Millimetric properties of gamma-ray burst host galaxies

We present millimetre (mm) and submillimetre (submm) photometry of a sample of five host galaxies of gamma-ray bursts (GRBs), obtained using the Max Planck Millimetre Bolometer (MAMBO2) array and Submillimetre Common-User Bolometer Array (SCUBA). These observations were obtained as part of an ongoing project to investigate the status of GRBs as indicators of star formation. Our targets include two of the most unusual GRB host galaxies, selected as likely candidate submm galaxies: the extremely red  ( R − K ≈ 5)  host of GRB 030115, and the extremely faint  ( R > 29.5)  host of GRB 020124. Neither of these galaxies is detected, but the deep upper limits for GRB 030115 impose constraints on its spectral energy distribution, requiring a warmer dust temperature than is commonly adopted for submillimetre galaxies (SMGs).
As a framework for interpreting these data, and for predicting the results of forthcoming submm surveys of Swift -derived host samples, we model the expected flux and redshift distributions based on luminosity functions of both submm galaxies and GRBs, assuming a direct proportionality between the GRB rate density and the global star formation rate density. We derive the effects of possible sources of uncertainty in these assumptions, including (1) introducing an anticorrelation between GRB rate and the global average metallicity, and (2) varying the dust temperature.     

Rest‐frame UV to optical X‐shooter spectrum of the gravitationally lensed galaxy “the 8 o'clock arc”: Dissection of its physical properties

We present the rest‐frame UV to optical spectrum of the gravitationally lensed galaxy, the “8 o'clock arc” at z = 2.735, obtained with the X‐shooter spectrograph. This is one of the rare comprehensive study of a high‐redshift star‐forming galaxy, usually not feasible due to the faintness of these objects. The spectrum of the 8 o'clock arc is rich in stellar and interstellar absorption features and in nebular emission features. Their analysis allowed us to derive most of the physical properties characterizing the galaxy. From HST images, we reconstruct the morphology of the arc in the source plane and confirm that we resolve a clump in rotation around the main core of galaxy in our X‐shooter spectrum (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

GRB‐selected galaxies

We describe the current status and recent results from our Swift/VLT legacy survey, a VLT Large Programme aimed at characterizing the host galaxies of a homogeneously selected sub‐sample of Swift gamma‐ray bursts (GRBs). The immediate goals are to determine the host luminosity function, study the effects of reddening, determine the fraction of Lyα emitters in the hosts, and obtain redshifts for targets without a reported one. We have defined a very carefully selected sample, obeying strict and well‐defined criteria: 68 targets in total. Among the preliminary results is a large optical detection rate, the lack of extremely red objects (only one possible case in the sample), and 10 new GRB redshifts with the mean redshift of the host sample assessed to be 〈z 〉 ≳ 2 (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A study of the kinematics of unusually H I‐rich galaxies

We examine the H I kinematics of the “Bluedisk” ensemble of 48 galaxies selected from the Sloan Digital Sky Survey and observed in H I with the Westerbork Synthesis Radio Telescope. The sample consists of 25 galaxies with a high H I mass fraction and a comparatively large control sample comprising 23 galaxies of comparable stellar mass, stellar mass surface density, redshift, and inclination. By studying the H I velocity fields of these galaxies, we investigate whether there are signatures of ongoing gas accretion: i.e. global asymmetries and indications for warping and kinematical lopsidedness. We find no enhanced kinematical asymmetries between the H I‐rich sample and the control sample galaxies, indicating no significant difference in kinematical signatures such as warping and lopsidedness. Furthermore, we find no difference in position angle and systemic velocity offset with respect to the optical between both sub‐samples. We therefore do not find compelling evidence for enhanced global asymmetry of the H I‐excess galaxies ensemble properties in comparison to the control sample galaxies. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The high redshift intergalactic and interstellar media with X‐shooter

I review here a few important questions that X‐shooter can help tackle and answer in the field of quasar absorption lines. This includes (i) determine the ionizing background and the physical state of the inter‐galactic medium (IGM) by analysing the characteristics of the Lyman‐α forest and the proximity effect; (ii) investigate the metal content of the high redshift IGM; (iii) study the small scale transverse correlation in the IGM by observing pairs of quasars with small separation in the sky; (iv) study the galaxy‐IGM relations by detecting the counterpart of damped Lyman‐α systems (DLAs) or determining the correlation between the properties of galaxies and absorption lines; (v) detect and characterize the long‐sought cold diffuse molecular (H₂ and CO) interstellar medium (ISM) of high redshift galaxies and study its dust content (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Modeling the total and polarized emission in evolving galaxies: “Spotty” magnetic structures

Future radio observations with the Square Kilometre Array (SKA) and its precursors will be sensitive to trace spiral galaxies and their magnetic field configurations up to redshift z ≈ 3. We suggest an evolutionary model for the magnetic configuration in star‐forming disk galaxies and simulate the magnetic field distribution, the total and polarized synchrotron emission, and the Faraday rotation measures for disk galaxies at z ≲ 3. Since details of dynamo action in young galaxies are quite uncertain, we model the dynamo action heuristically relying only on well‐established ideas of the form and evolution of magnetic fields produced by the mean‐field dynamo in a thin disk. We assume a small‐scale seed field which is then amplified by the small‐scale turbulent dynamo up to energy equipartition with kinetic energy of turbulence. The large‐scale galactic dynamo starts from seed fields of 100 pc and an averaged regular field strength of 0.02 μG, which then evolves to a “spotty” magnetic field configuration in about 0.8 Gyr with scales of about one kpc and an averaged regular field strength of 0.6 μG. The evolution of these magnetic spots is simulated under the influence of star formation, dynamo action, stretching by differential rotation of the disk, and turbulent diffusion. The evolution of the regular magnetic field in a disk of a spiral galaxy, as well as the expected total intensity, linear polarization and Faraday rotation are simulated in the rest frame of a galaxy at 5GHz and 150 MHz and in the rest frame of the observer at 150 MHz. We present the corresponding maps for several epochs after disk formation. Dynamo theory predicts the generation of large‐scale coherent field patterns (“modes”). The timescale of this process is comparable to that of the galaxy age. Many galaxies are expected not to host fully coherent fields at the present epoch, especially those which suffered from major mergers or interactions with other galaxies. A comparison of our predictions with existing observations of spiral galaxies is given and discussed (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Absorption spectroscopy of gamma‐ray burst afterglows: Probing the GRB line of sight

GRB absorption spectroscopy opened up a new window in the study of the high redshift Universe, especially with the launch of the Swift satellite and the quick and precise localization of the afterglow. Eight‐meter class telescopes can be repointed within a few hours from the GRB, enabling the acquisition of high signal‐to‐noise ratio and high resolution afterglow spectra. In this paper I will give a short review of what we learned through this technique, and I will present some of the first results obtained with the X‐shooter spectrograph (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Studying the SN‐GRB connection with X‐shooter: The GRB 100316D / SN 2010bh case

During the last ten years, observations of long‐duration gamma‐ray bursts brought to the conclusion that at least a fraction of them is associated with bright supernovae of type Ib/c. In this talk, after a short review on the previously observed GRB‐SN connection cases, we present the recent case of GRB 100316/SN 2010bh. In particular, during the observational campaign of SN 2010bh, a pivotal role was played by VLT/X‐shooter, sampling with unique high quality data the spectral energy distribution of the early evolution phases from the UV to the K band (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Integral field spectroscopy of QSO host galaxies

We describe a project to study the state of the ISM in ∼20 low redshift (z < 0.3) QSO host galaxies observed with the PMAS integral field spectrograph. We describe the development of the method to access the stellar and gas components of the spectrum without the strong nuclear emission, in order to access the host galaxy properties in the central region. It shows that integral field spectroscopy promises to be very efficient in studying the gas distribution and its velocity field, and also the spatially resolved stellar population in the host galaxies of luminous AGN. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Spatial and kinematical lopsidedness of atomic hydrogen in the Ursa Major group of galaxies

We have carried out the harmonic analysis of the atomic hydrogen (H  i ) surface density maps and the velocity fields for 11 galaxies belonging to the Ursa Major group, over a radial range of 4–6 disc scalelengths in each galaxy. This analysis gives the radial variation of spatial lopsidedness, quantified by the Fourier amplitude A ₁ of the   m = 1  component normalized to the average value. The kinematical analysis gives a value for the elongation of the potential to be ∼10 per cent. The mean amplitude of spatial lopsidedness is found to be ∼0.14 in the inner disc, similar to the field galaxies, and is smaller by a factor of ∼2 compared to the Eridanus group galaxies. It is also shown that the average value of A ₁ does not increase with the Hubble type, contrary to what is seen in field galaxies. We argue that the physical origin of lopsidedness in the Ursa Major group of galaxies is tidal interactions, albeit weaker and less frequent than in Eridanus. Thus systematic studies of lopsidedness in groups of galaxies can provide dynamical clues regarding the interactions and evolution of galaxies in a group environment.     

Comparison of dust‐to‐gas ratios in luminous,ultraluminous, and hyperluminous infrared galaxies

The dust‐to‐gas ratios in three different samples of luminous, ultraluminous, and hyperluminous infrared galaxies are calculated by modelling their radio to soft X‐ray spectral energy distributions (SED) using composite models which account for the photoionizing radiation from H II regions, starbursts, or AGNs, and for shocks. The models are limited to a set which broadly reproduces the mid‐IR fine structure line ratios of local, IR bright, starburst galaxies. The results show that two types of clouds contribute to the IR emission. Those characterized by low shock velocities and low preshock densities explain the far‐IR dust emission, while those with higher velocities and densities contribute to the mid‐IR dust emission. Clouds with shock velocities of 500 km s^–1 prevail in hyperluminous infrared galaxies. An AGN is found in nearly all of the ultraluminous infrared galaxies and in half of the luminous infrared galaxies of the sample. High IR luminosities depend on dust‐to‐gas ratios as high as ∼0.1 by mass, however most hyperluminous IR galaxies show dustto‐gas ratios much lower than those calculated for the luminous and ultraluminous IR galaxies. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

OASIS high‐resolution integral field spectroscopy of the SAURON ellipticals and lenticulars

We present a summary of high‐spatial resolution follow‐up observations of the elliptical (E) and lenticular (S0) galaxies in the SAURON survey using the OASIS integral field spectrograph. The OASIS observations explore the central 8″ × 10″ regions of these galaxies using a spatial sampling four times higher than SAURON, often revealing previously undiscovered features. Around 75% (31/48) of the SAURON E/S0s with central velocity dispersion ≳ 120 km s⁻¹ were observed with OASIS, covering well the original SAURON representative sample.We present here an overview of this follow‐up survey, and some preliminary results on individual objects, including a previously unreported counter‐rotating core in NGC4382; the decoupled stellar and gas velocity fields of NGC2768; and the strong age gradient towards the centre of NGC3489. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The isolated dSph galaxy KKs3 in the local Hubble flow

We present SALT spectroscopy of a globular cluster in the center of the nearby isolated dSph galaxy KKs3 situated at a distance of 2.12 Mpc. Its heliocentric radial velocity is 316 ± 7 km s^–1 that corresponds to V_LG = 112 km s^–1 in the Local Group (LG) reference frame. We use its distance and velocity along with the data on other 35 field galaxies in the proximity of the LG to trace the local Hubble flow. The following basic properties of the local field galaxies are briefly discusse: morphology, absolute magnitudes, average surface brightnesses, specific star formation rates, and hydrogen mass‐to‐stellar mass ratios. Surprisingly, the sample of the neighboring isolated galaxies displays no signs of compression under the influence of the expanding Local Void. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)