Prof. Niranjan Thatte

Abstract:

KMOS (K-Band Multi Object Spectrograph) is a novel integral field spectrograph installed in the VLT's ANTU unit. The instrument offers an ability to observe 24 2.8"$\times$2.8" sub-fields positionable within a 7.2' patrol field, each sub-field producing a spectrum with a 14$\times$14-pixel spatial resolution. The main science drivers for KMOS are the study of galaxies, star formation, and molecular clouds, but its ability to simultaneously measure spectra of multiple stars makes KMOS an interesting instrument for exoplanet atmosphere characterization via transmission spectroscopy. We set to test whether transmission spectroscopy is practical with KMOS, and what are the conditions required to achieve the photometric precision needed, based on observations of a partial transit of WASP-19b, and full transits of GJ 1214b and HD 209458b. Our analysis uses the simultaneously observed comparison stars to reduce the effects from instrumental and atmospheric sources, and Gaussian processes to model the residual systematics. We show that KMOS can, in theory, deliver the photometric precision required for transmission spectroscopy. However, this is shown to require a) pre-imaging to ensure accurate centering and b) a very stable night with optimal observing conditions (seeing $\sim$0.8"). Combining these two factors with the need to observe several transits, each with a sufficient out-of-transit baseline (and with the fact that similar or better precision can be reached with telescopes and instruments with smaller pressure,) we conclude that transmission spectroscopy is not the optimal science case to take advantage of the abilities offered by KMOS and VLT.

Abstract:

We present HSIM: a dedicated pipeline for simulating observations with the HARMONI integral field spectrograph on the European Extremely Large Telescope. HSIM takes high spectral and spatial resolution input data-cubes, encoding physical descriptions of astrophysical sources, and generates mock observed data-cubes. The simulations incorporate detailed models of the sky, telescope and instrument to produce realistic mock data. Further, we employ a new method of incorporating the strongly wavelength dependent adaptive optics point spread functions. HSIM provides a step beyond traditional exposure time calculators and allows us to both predict the feasibility of a given observing programme with HARMONI, as well as perform instrument design trade-offs. In this paper we concentrate on quantitative measures of the feasibility of planned observations. We give a detailed description of HSIM and present two studies: estimates of point source sensitivities along with simulations of star-forming emission-line galaxies at $z\sim 2-3$. We show that HARMONI will provide exquisite resolved spectroscopy of these objects on sub-kpc scales, probing and deriving properties of individual star-forming regions.

Abstract:

We present Herschel far-IR photometry and spectroscopy as well as ground-based CO observations of an intermediate redshift (0.21 ≤ z ≤ 0.88) sample of Herschel-selected (ultra)-luminous infrared galaxies (L IR > 10^11.5 L ☉). With these measurements, we trace the dust continuum, far-IR atomic line emission, in particular [C II] 157.7 μm, as well as the molecular gas of z ~ 0.3 luminous and ultraluminous infrared galaxies (LIRGs and ULIRGs) and perform a detailed investigation of the interstellar medium of the population. We find that the majority of Herschel-selected intermediate redshift (U)LIRGs have L C II /L FIR ratios that are a factor of about 10 higher than that of local ULIRGs and comparable to that of local normal and high-z star-forming galaxies. Using our sample to bridge local and high-z [C II] observations, we find that the majority of galaxies at all redshifts and all luminosities follow an L C II –L FIR relation with a slope of unity, from which local ULIRGs and high- z active-galactic-nucleus-dominated sources are clear outliers. We also confirm that the strong anti-correlation between the L C II /L FIR ratio and the far-IR color L 60/L 100 observed in the local universe holds over a broad range of redshifts and luminosities, in the sense that warmer sources exhibit lower L C II /L FIR at any epoch. Intermediate redshift ULIRGs are also characterized by large molecular gas reservoirs and by lower star formation efficiencies compared to that of local ULIRGs. The high L C II /L FIR ratios, the moderate star formation efficiencies (L IR/$L^{\prime }_{\rm CO}$ or L IR/$M_{\rm H_{\rm 2}}$), and the relatively low dust temperatures of our sample (which are also common characteristics of high-z star-forming galaxies with ULIRG-like luminosities) indicate that the evolution of the physical properties of (U)LIRGs between the present day and z > 1 is already significant by z ~ 0.3.