Star-Forming Regions near GRB 990123

We reduced the Hubble Space Telescope Space Telescope Imaging Spectrograph images of the gamma-ray burst GRB 990123 that were obtained on 8-9 February 1999 and find V_0 = 25.36 +/- 0.10, which corresponds to a flux of 0.258 +/- 0.023 micro-Jy for the optical transient 16.644 days after the burst's peak. The probable host galaxy has V_0 = 24.25 +/- 0.07 (= 0.716 +/- 0.046 micro-Jy) and the optical transient is located 0.65 arcseconds (= 5.5 kpc) south of the galaxy's nucleus. We fit and subtracted a scaled point-spread function to the optical transient and found evidence for three bright knots situated within 0.5 arcseconds (= 4.3 kpc) of the optical transient. Each knot has V_0 ~ 28.1 +/- 0.3, a rest-frame V-band luminosity of between approximately 5e8 L_Sun and 8e8 L_Sun, and a star-formation rate of at least 0.1-0.2 Solar masses per year. The knots are centrally concentrated with full-width at half-maximum of approximately 0.17 arcseconds (= 1.5 kpc). Their sizes and luminosities are consistent with their being star-forming regions. The optical transient is located 0.15 arcseconds (= 1.3 kpc) southeast of the centre of one of these knots.Comment: 4 pages, 2 figures, to appear in Astronomy & Astrophysics Letter

Light Curve Properties of Supernovae Associated With Gamma-ray Bursts

Little is known about the diversity in the light curves of GRB-SNe, including whether the light curve of SN 1998bw can be used as a representative template or whether there is a luminosity-decline rate relation akin to that of SNe Ia. In this paper, we aim to obtain well-constrained light curves of GRB-SNe without the assumption of empirical or parametric templates and to investigate whether the peak brightness correlates with other parameters such as the light curve shape or the time of peak. We select eight SNe in the redshift range 0.0085 to 0.606, which are firmly associated with GRBs. The light curves of these GRB-SNe are well sampled across the peak. Afterglow and host galaxy contributions are subtracted and dust reddening is corrected for. Low-order polynomial functions are fitted to the light curves. A K-correction is applied to transform the light curves into the rest frame V band. GRB-SNe follow a luminosity-decline rate relation similar to the Phillips relation for SNe Ia, with $M_{V,peak} = 1.59^{+0.28}_{-0.24} \Delta m_{V,15} - 20.61^{+0.19}_{-0.22}$, with $\chi^2 = 5.2$ for 6 dof and $M_{V,peak}$ and $\Delta m_{V,15}$ being the peak magnitude and decline rate in V band. This luminosity-decline rate relation is tighter than the k-s relation, where k and s are the factors describing the relative brightness and width to the light curve of SN 1998bw. The peak luminosities of GRB-SNe are also correlated with the time of peak: the brighter the GRB-SN, the longer the rise time. The light curve of SN 1998bw stretched around the time of explosion can be used as a template for GRB-SNe with reasonable confidence, but stretching around the peak produces better results. The existence of such a relation provides a new constraint on GRB explosion models. GRB-SNe can be used as standardizable candles to measure cosmological distances and constrain cosmological parameters.Comment: 17 pages, 15 figures. Submitted to Astronomy & Astrophysics on July 4, 201

Maximally dusty star-forming galaxies: Supernova dust production and recycling in Local Group and high-redshift galaxies

Motivated by recent observations suggesting that core-collapse supernovae may on average produce ~0.3 M_sun of dust, we explore a simple dust production scenario which applies to star-forming galaxies in the local environment (the Magellanic Clouds and possibly the Milky Way) as well as to high redshift (sub- millimeter, QSO, Lyman break) galaxies. We assume that the net dust destruction (due to supernova reverse shock, shocks in the interstellar medium, or astration) is negligible on a timescale of 1 Gyr, in which case the dust mass can be estimated as 0.004 times the star-formation rate (for a Chabrier IMF) multiplied by the duration of the star-formation episode. The model can account for observed dust masses over four orders of magnitude and across the redshift range 0-8.4, with dust production rates spanning five orders of magnitudes. This suggests that star-forming galaxies may be seen as maximally dusty, in the sense that a dominant fraction of the dust-forming elements forged in a supernova eventually will go into the solid phase. In turn, this indicates little destruction of supernova dust or almost complete replenishment, on a short time scale, of any dust that is destroyed.Comment: 14 pages, 3 figures, 1 table, accepted for ApJ

The Fundamental Plane at z=0.18

We present preliminary results regarding the Fundamental Plane (FP) for galaxies in the two rich clusters Abell 665 and Abell 2218. Both clusters have a redshift of 0.18. We have compared the FP for A665 and A2218, and for the cluster CL0024+16 at z=0.39, with the FP for the Coma cluster. The scatter around the FP is similar for all four clusters. There may be indications that the slope of the FP is more shallow for the intermediate redshift clusters than for the Coma cluster. More complete samples of galaxies in intermediate redshift clusters are needed to map in detail the possible change of the slope as function of redshift. The mass-to-light (M/L) ratio as measured by the FP changes with redshift. At z=0.18 the M/L ratio (in Gunn r) is 16+-9% smaller than for the Coma cluster. Together with earlier results reported for CL0024+16 this implies that the M/L ratio changes with redshift as Delta log M/L_r ~ -0.4 Delta z. The results presented here are in agreement with passive evolution of a stellar population, which formed at a redshift larger than one. However, the possible presence of more recent bursts of star formation complicates the interpretation of the data.Comment: 10 pages, 5 figures included, LaTeX style lamuphys.sty To appear in the proceedings of the 3rd ESO-VLT Workshop Galaxy Scaling Relations, eds. da Costa et al., Springe

A break in the high-redshift stellar mass Tully-Fisher relation

We investigate the stellar-mass Tully-Fisher relation (TFR) between the stellar mass and the integrated gas velocity dispersion, quantified by the kinematic estimator S_0.5 measured from strong emission lines in spectra of galaxies at 0<z<5. We combine luminosity-selected galaxies (`high-luminosity sample') with galaxies selected in other ways (`low-luminosity sample') to cover a range in stellar mass that spans almost five orders of magnitude: 7.0 < log M* < 11.5. We find that the logarithmic power-law slope and normalisation of the TFR are independent of redshift out to z~3. The scatter in the TFR is <0.5 dex such that the gas velocity dispersion can be used as a proxy for the stellar mass of a galaxy independently of its redshift. At z>3 the scatter increases and the existence of a correlation is not obvious. The high-luminosity sample exhibits a flatter slope of 1.5$\pm$0.2 at z<3 compared to the low-luminosity sample slope of 2.9$\pm$0.3, suggesting a turnover in the TFR. The combined sample is well fit with a break in the TFR at a characteristic stellar mass scale of M*~10$^{10}$ M$_{\odot}$, with no significant evolution out to z~3. We demonstrate that a break in the TFR with a steeper slope at the low-mass end is a natural consequence of galaxy models with a mass-dependent stellar to halo-mass ratio.Comment: 12 pages, Accepted for publication in MNRA

The extinction curve of the lensing galaxy of B1152+199 at z=0.44

We present UBVRIz' photometry of the gravitational lens candidate CLASS B1152+119 obtained with the Nordic Optical Telescope. The two QSO components are resolved in the B, V, R, I and z' bands confirming the lensing nature of the system. The z=0.44 lens galaxy is clearly detected in B, R, I and z' and its position is found to be almost coincident with the faint QSO image which is heavily extincted (relative to the brighter QSO image) by dust in the lens galaxy. The extinction curve of the lens galaxy derived from the relative photometry is well fitted by a Galactic extinction law with 1.3 < R_V < 2.0 and E(B-V) ~ 1. From a simple model of the system we predict a time delay of ~ 60 days.Comment: 6 pages, 7 figures, accepted for publication in Astronomy and Astrophysic

Cosmological Parameters From Supernovae Associated With Gamma-ray Bursts

We report estimates of the cosmological parameters $\Omega_m$ and $\Omega_{\Lambda}$ obtained using supernovae (SNe) associated with gamma-ray bursts (GRBs) at redshifts up to 0.606. Eight high-fidelity GRB-SNe with well-sampled light curves across the peak are used. We correct their peak magnitudes for a luminosity-decline rate relation to turn them into accurate standard candles with dispersion $\sigma = 0.18$ mag. We also estimate the peculiar velocity of the low-redshift host galaxy of SN 1998bw, using constrained cosmological simulations. In a flat universe, the resulting Hubble diagram leads to best-fit cosmological parameters of $(\Omega_m, \Omega_{\Lambda}) = (0.58^{+0.22}_{-0.25},0.42 ^{+0.25}_{-0.22})$. This exploratory study suggests that GRB-SNe can potentially be used as standardizable candles to high redshifts to measure distances in the universe and constrain cosmological parameters.Comment: 7 pages, 3 figures, Accepted for publication in ApJ

Distribution functions for clusters of galaxies from N-body simulations

We present the results of an attempt to adapt the distribution function formalism to characterize large-scale structures like clusters of galaxies that form in a cosmological N-body simulation. While galaxy clusters are systems that are not strictly in equilibrium, we show that their evolution can nevertheless be studied using a physically motivated extension of the language of equilibrium stellar dynamics. Restricting our analysis to the virialized region, a prescription to limit the accessible phase-space is presented, which permits the construction of both the isotropic and the anisotropic distribution functions $f(E)$ and $f(E,L)$. The method is applied to models extracted from a catalogue of simulated clusters. Clusters evolved in open and flat background cosmologies are followed during the course of their evolution, and are found to transit through a sequence of what we define as `quasi-equilibrium' states. An interesting feature is that the computed $f(E)$ is well fit by an exponential form. We conclude that the dynamical evolution of a cluster, undergoing relaxation punctuated by interactions and violent mergers with consequent energy-exchange, can be studied both in a qualitative and quantitative fashion by following the time evolution of $f(E)$.Comment: 16 pages, LaTeX file, all figures included, revised version, accepted for publication in MNRA

Shaping the dust mass - star-formation rate relation

There is a remarkably tight relation between the observationally inferred dust masses and star-formation rates (SFRs) of SDSS galaxies, Mdust $\propto$ SFR$^{1.11}$ (Da Cunha et al. 2010). Here we extend the Mdust-SFR relation to the high end and show that it bends over at very large SFRs (i.e., dust masses are lower than predicted for a given SFR). We identify several distinct evolutionary processes in the diagram: (1) A star-bursting phase in which dust builds up rapidly at early times. The maximum attainable dust mass in this process is the cause of the bend-over of the relation. A high dust-formation efficiency, a bottom-light initial mass function, and negligible supernova shock dust destruction are required to produce sufficiently high dust masses. (2) A quiescent star-forming phase in which the subsequent parallel decline in dust mass and SFR gives rise to the Mdust-SFR relation, through astration and dust destruction. The dust-to-gas ratio is approximately constant along the relation. We show that the power-law slope of the Mdust-SFR relation is inversely proportional to the global Schmidt-Kennicutt law exponent (i.e., $\sim 0.9$) in simple chemical evolution models. (3) A quenching phase which causes star formation to drop while the dust mass stays roughly constant or drops proportionally. Combined with merging, these processes, as well as the range in total baryonic mass, give rise to a complex population of the diagram which adds significant scatter to the original Mdust-SFR relation. (4) At very high redshifts, a population of galaxies located significantly below the local relation is predicted.Comment: 5 pages, 1 figure, ApJL, in pres