Dr Aprajita Verma

Abstract:

We present ∼0″5 resolution near-infrared integral field spectroscopy of the Hα line emission of 14 z ∼ 2 UV-selected BM/BX galaxies, obtained with SINFONI at the ESO Very Large Telescope. The average Hα half-light radius is r1/2 ≈4 h70-1 kpc, and line emission is detected over ≳20 h70-1 kpc in several sources. In nine galaxies, we detect spatially resolved velocity gradients, from 40 to 410 km s-1 over ∼10 h70-1 kpc. The kinematics of the larger systems are generally consistent with orbital motions. Four galaxies are well described by rotating clumpy disks, and we extracted rotation curves out to radii ≳10 h 70-1 kpc. One or two galaxies exhibit signatures more consistent with mergers. Analyzing all 14 galaxies in the framework of rotating disks, we infer mean inclination- and beam-corrected maximum circular velocities of vc ∼ 180 ± 90 km s-1 and dynamical masses from ∼0.5 to 25 × 1010 h70-1 M ⊙ within r1/2- The specific angular momenta of our BM/BX galaxies are similar to those of local late-type galaxies. Moreover, the specific angular momenta of their baryons are comparable to those of their dark matter halos. Extrapolating from the average vc at 10 h 70-1 kpc, the virial mass of the typical halo of a galaxy in our sample is 1011.7±0.5 h70-1 M ⊙. Kinematic modeling of the three best cases implies a ratio of vc to local velocity dispersion vc/σ ∼ 2-4 and, accordingly, a large geometric thickness. We argue that this suggests a mass accretion (alternatively, gas exhaustion) timescale of ∼500 Myr. We also argue that if our BM/BX galaxies were initially gas-rich, their clumpy disks would subsequently lose their angular momentum and form compact bulges on a timescale of ∼1 Gyr. © 2006. The American Astronomical Socieity. All rights reserved.

Abstract:

We present a deep photometric (B- and R-band) catalog and an associated spectroscopic redshift survey conducted in the vicinity of the Hubble Deep Field-South. The spectroscopy yields 53 extragalactic redshifts in the range 0 < z < 1.4, substantially increasing the body of spectroscopic work in this field to over 200 objects. The targets are selected from deep Anglo-Australian Telescope prime-focus images complete to R < 24, and the spectroscopy is 5 0% complete at R = 23. There is now strong evidence for a rich cluster at z ≃ 0.5 8 flanking the Wide Field Planetary Camera 2 field, which is consistent with a known absorber of the bright QSO in this field. We find that photometric redshifts of z < 1 galaxies in this field based on Hubble Space Telescope data are accurate to σ z/(1 + z) = 0.03 (albeit with small number statistics). The observations were carried out as a community service for Hubble Deep Field science in order to demonstrate the first use of the nod-and-shuffle technique with a classical multiobject spectrograph and to test the use of microslits for ultrahigh multiplex observations along with a new volume phase holographic grism and deep-depletion CCD. The reduction of this new type of data is also described. © 2006. The American Astronomical Society. All rights reserved.

Abstract:

Some of the most 'active' galaxies in the Universe are obscured by large quantities of dust and emit a substantial fraction of their bolometric luminosity in the infrared. Observations of these infrared luminous galaxies with the Infrared Space Observatory (ISO) have provided a relatively unabsorbed view to the sources fuelling this active emission. The improved sensitivity, spatial resolution and spectroscopic capability of ISO over its predecessor Infrared Astronomical Satellite (IRAS) of enabled significant advances in the understanding of the infrared properties of active galaxies. ISO surveyed a wide range of active galaxies which, in the context of this review, includes those powered by intense bursts of star formation as well as those containing a dominant active galactic nucleus (AGN). Mid-infrared imaging resolved for the first time the dust enshrouded nuclei in many nearby galaxies, while a new era in infrared spectroscopy was opened by probing a wealth of atomic, ionic and molecular lines as well as broad band features in the mid-and farinfrared. This was particularly useful, since it resulted in the understanding of the power production, excitation and fuelling mechanisms in the nuclei of active galaxies including the intriguing but so far elusive ultraluminous infrared galaxies. Detailed studies of various classes of AGN and quasars greatly improved our understanding of the unification scenario. Far-infrared imaging and photometry revealed the presence of a new very cold dust component in galaxies and furthered our knowledge of the far-infrared properties of faint starbursts, ULIGs and quasars. We summarise almost nine years of key results based on ISO data spanning the full range of luminosity and type of active galaxies. © 2005 Springer.

Abstract:

Infrared bright galaxies (LIRGs and ULIRGs) represent the bulk of the cosmic infrared background and play a major role in the cosmic star formation and accretion histories. For this reason they have been subject of intensive studies at all wavelengths. However, being very dusty galaxies, one of the key wavelength range to understand their evolutionary stages and the physic involved, is the Mid-Far-Infrared and sub-millimeter window. Previous (IRAS and ISO) and current (SPITZER) infrared missions, already shed light on the nature and the evolution of these galaxies, but still many phenomena lack of a complete understanding. For example, the processes triggering the starburst and AGN activities as well as trends with the interaction stage, are not well established yet, partially because at FIR wavelengths it has not been possible so far to spatially resolve these different components even in nearby objects. With its passively cooled 3.5 meter telescope, HERSCHEL will offer this opportunity for the first time. In particular, the PACS instrument, is unique for tackling some important open issues thanks to its spectro imaging capability at FIR wavelengths. We will illustrate some of these exciting new opportunities using examples from the Guaranteed Time program on infrared bright galaxies, that is currently being developed. ISO has undoubtedly shown that the use of Mid-Far-infrared spectroscopy is a powerful tool for establishing the physical conditions of the ISM and separating the starburst and AGN activity contributions which often coexist in (U)LIRGs. However, such a coexistence makes the central regions of (U)LIRG very peculiar such that we expect the ISM in their central regions to be very different than in normal star-forming galaxies. One known example is the fact that ultra luminous infrared galaxies have less [CII] emission w.r.t. the total FIR emission ([CII] deficiency) than what is found in normal galaxies. This result, found in several studies based on ISO spectroscopy, points towards a different heating/cooling balance of the ISM in infrared bright galaxies, but the causes and the related physic remain unknown. With PACS it will be possible to take full resolution complete PACS scans of representative nearby sources such that we can probe the ISM physics in central starbursts, the circum-nuclear molecular rings, disks and winds, separately. Moreover, a survey of the most important FIR structure lines will become feasable for large samples spanning from starburst, AGNs and obscured objects, at local and intermediate redshift. Observations with the PACS photometric camera in its three bands (70,110 and 170 μm) will complement the science possible with the integral field spectroscopy, because HERSCHEL will be able to resolve for the first time individual dust enshrouded activity knots, i.e. the place where star formation is triggered, to locate the starburst regions and their relative contributions in interacting systems. Due to the unprecedent spatial resolution HERSCHEL provides at FIR and sub-millimeter wavelengths and the improved sensitivities of its instruments, we expect that a significant part of HERSCHEL observing time will be spent on the study of high redshift galaxies. Detailed studies of nearby templates, as illustrated here, will significantly contribute in understanding in detail the physics governing the diagnostic diagrams and the change in spectral characteristics which are the basic tools for studying unresolved galaxies at high redshift. © 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Abstract:

Some of the most 'active' galaxies in the Universe are obscured by large quantities of dust and emit a substantial fraction of their bolometric luminosity in the infrared. Observations of these infrared luminous galaxies with the Infrared Space Observatory (ISO) have provided a relatively unabsorbed view to the sources fuelling this active emission. The improved sensitivity, spatial resolution and spectroscopic capability of ISO over its predecessor Infrared Astronomical Satellite (IRAS) of enabled significant advances in the understanding of the infrared properties of active galaxies. ISO surveyed a wide range of active galaxies which, in the context of this review, includes those powered by intense bursts of star formation as well as those containing a dominant active galactic nucleus (AGN). Mid-infrared imaging resolved for the first time the dust enshrouded nuclei in many nearby galaxies, while a new era in infrared spectroscopy was opened by probing a wealth of atomic, ionic and molecular lines as well as broad band features in the mid- and far-infrared. This was particularly useful, since it resulted in the understanding of the power production, excitation and fuelling mechanisms in the nuclei of active galaxies including the intriguing but so far elusive ultraluminous infrared galaxies. Detailed studies of various classes of AGN and quasars greatly improved our understanding of the unification scenario. Far-infrared imaging and photometry revealed the presence of a new very cold dust component in galaxies and furthered our knowledge of the far-infrared properties of faint starbursts, ULIGs and quasars. We summarise almost nine years of key results based on ISO data spanning the full range of luminosity and type of active galaxies. © Springer 2005.