arXiv subjects

Tanmoy Laskar

Publications and source records attributed to Tanmoy Laskar.

79 records · Page 5Linked to original sources

arXiv2011

Exploring The Galaxy Mass-Metallicity Relation at 3 < z < 5

Long-duration gamma-ray bursts (GRBs) provide a premier tool for studying high-redshift star-forming galaxies thanks to their extreme brightness and association with massive stars. Here we use GRBs to study the galaxy mass-metallicity (M*-Z) relation at z~3-5, where conventional direct metallicity measurements are extremely challenging. We use the interstellar medium metallicities of long-duration GRB hosts derived from afterglow absorption pectroscopy (Z~0.01-1 solar), in conjunction with host galaxy stellar masses determined from deep Spitzer 3.6 micron observations of 20 GRB hosts. We detect about 1/4 of the hosts with I-band absolute magnitudes, M ~ -21.5 to -22.5 AB mag, and place a limit of M>-19 mag on the remaining hosts from a stacking analysis. Using a conservative range of mass-to-light ratios for simple stellar populations (with ages of 70 Myr to ~ 2 Gyr), we infer the host stellar masses and present the galaxy mass-metallicity measurements at z ~ 3-5 ( ~ 3.5). We find that the detected GRB hosts, with M* ~ 2e10 solar masses, display a wide range of metallicities, but that the mean metallicity at this mass scale, Z~ 0.1 solar, is lower than measurements at z < 3. Combined with stacking of the non-detected hosts (with M* < 4e9 solar masses and Z < 0.03 solar), we find evidence for the existence of an M*-Z relation at z ~ 3.5 and continued evolution of this relation to systematically lower metallicities from z ~ 2.

astro-ph.CO↗

arXiv2011

Exploring the Galaxy Mass-Metallicity Relation at z~3-5

Long-duration gamma-ray bursts (GRBs) provide a premier tool for studying high-redshift star-forming galaxies thanks to their extreme brightness and association with massive stars. Here we use GRBs to study the galaxy stellar mass-metallicity (M*-Z) relation at z~3-5, where conventional direct metallicity measurements are extremely challenging. We use the ISM metallicities of LGRB hosts derived from afterglow absorption spectroscopy (Z~0.01-1 solar), in conjunction with host galaxy stellar masses determined from deep Spitzer 3.6 micron observations of 20 GRB hosts. We detect about 1/4 of the hosts with I-band magnitudes ~ -21.5 to -22.5 AB mag, and place a limit of M > -19 mag on the remaining hosts from a stacking analysis. Using these observations, we present the first rest-frame optical luminosity distribution of long GRB hosts at z>3 and find that it is similar to the distribution of long GRB hosts at z~1. In comparison to Lyman-break galaxies at the same redshift, GRB hosts are generally fainter, but the sample is too small to rule out an overall similar luminosity function. On the other hand, the GRB hosts appear to be more luminous than the population of Lyman-alpha emitters at z~3-4. Using a conservative range of mass-to-light ratios for simple stellar populations (with ages of 70 Myr to ~2 Gyr), we infer the host stellar masses and present mass-metallicity measurements at z~3-5 ( ~ 3.5). We find that the detected GRB hosts, with M*~2e10 solar masses, display a wide range of metallicities, but that the mean metallicity at this mass scale, Z~0.1 solar, is lower than measurements at z<3. Combined with stacking of the non-detected hosts with M*< 3e9 solar masses and Z<0.03 solar, we find evidence for the existence of an M*-Z relation at z~3.5 and continued evolution of this relation to systematically lower metallicities from z~2.

astro-ph.CO↗

arXiv2009

The Metallicity of the Pleiades

We have measured the abundances of Fe, Si, Ni, Ti, and Na in 20 Pleiads with \teff values near solar and with low \vsini using high-resolution, high signal-to-noise echelle spectra. We have validated our procedures by also analyzing 10 field stars of a range of temperatures and metallicities that were observed by \citet{Vale05}. Our result for the Pleiades is [Fe/H] = $+0.03\pm0.02\pm0.05$ (statistical and systematic). The average of published measurements for the Pleiades is $+0.042\pm0.021$.

astro-ph.SR↗

arXiv2009

The Metallicity of the HD 98800 System

Pre-main sequence (PMS) binaries and multiples enable critical tests of stellar models if masses, metallicities, and luminosities of the component stars are known. We have analyzed high-resolution, high signal-to-noise echelle spectra of the quadruple-star system HD 98800 and using spectrum synthesis, computed fits to the composite spectrum for a full range of plausible stellar parameters for the components. We consistently find that sub-solar metallicity yields fits with lower $χ^2$ values, with an overall best-fit of $[M/H] = -0.20\pm0.10$. This metallicity appears to be consistent with PMS evolutionary tracks for the measured masses and luminosities of the components of HD 98800 but additional constraints on the system and modelling are needed.

astro-ph.SR↗

arXiv2008

Restarting engine in an X-shaped radio galaxy

J2018-556, an X-shaped FR-I radio galaxy provides a unique opportunity to discuss the formation scenarios for the extended structures seen in this class of radio sources. An understanding of the origin of X-shaped source structures has important implications for radio galaxy models as well as black hole-black hole mergers. Guided by our ATCA radio continuum observations of J2018-556 we discuss evidence in support of 'wings' forming as a result of a redirection of backflows by asymmetric gas distribution associated with the host galaxy. Formation models invoking interaction between backflows with asymmetric environments seem the preferred model for X-shaped radio sources despite apparent discoveries of X-shaped FR-I radio sources.

astro-ph↗

arXiv2008

Dust sputtering by Reverse Shocks in Supernova Remnants

We consider sputtering of dust grains, believed to be formed in cooling supernovae ejecta, under the influence of reverse shocks. In the regime of self-similar evolution of reverse shocks, we can follow the evolution of ejecta density and temperature analytically as a function of time in different parts of the ejecta, and calculate the sputtering rate of graphite and silicate grains embedded in the ejecta as they encounter the reverse shock. Through analytic (1D) calculations, we find that a fraction of dust mass ($ 1\hbox{--}20$% for silicates and %$\le 5$% for graphites) can be sputtered by reverse shocks, the fraction varying with the grain size distribution and the steepness of the density profile of the ejecta mass. It is expected that many more grains will get sputtered in the region between the forward and reverse shocks, so that our analytical results provide a lower limit to the destroyed fraction of dust mass.

astro-ph↗

arXiv2007

Direction Dependent Non-gaussianity in High-z Supernova Data

The most detailed constraints on the accelerating expansion of the universe and details of nature of dark energy are derived from the high redshift supernova data, assuming that the errors in the measurements are Gaussian in nature. There is a possibility that there are direction dependent systematics in the data, either due to uncorrected, known physical processes or because there are tiny departures from the cosmological principle, making the universe slightly anisotropic. To investigate this possibility we introduce a statistic based on the extreme value theory and apply it to the gold data set from Riess et al. (2004). Our analysis indicates a systematic, direction dependent non-gaussianity at about one sigma level.

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