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Black Hole

Lensing of space time around a black hole. At Oxford we study black holes observationally and theoretically on all size and time scales - it is some of our core work.

Credit: ALAIN RIAZUELO, IAP/UPMC/CNRS. CLICK HERE TO VIEW MORE IMAGES.

Dr Aprajita Verma

Senior Research Fellow

Research theme

  • Astronomy and astrophysics

Sub department

  • Astrophysics

Research groups

  • Zooniverse
  • Astronomical instrumentation
  • Galaxy formation and evolution
  • Rubin-LSST
  • Extremely Large Telescope
aprajita.verma@physics.ox.ac.uk
Telephone: 01865 (2)73374
Denys Wilkinson Building, room 760
  • About
  • Outreach
  • Teaching
  • Publications

Far-infrared line deficits in galaxies with extreme L /M ratios

Astrophysical Journal Letters 728:1 PART II (2011)

Authors:

J Graciá-Carpio, E Sturm, S Hailey-Dunsheath, A Contursi, A Poglitsch, R Genzel, R Davies, H Feuchtgruber, JA De Jong, D Lutz, LJ Tacconi, J Fischer, E González-Alfonso, A Sternberg, A Verma, N Christopher

Abstract:

We report initial results from the far-infrared fine structure line observations of a sample of 44 local starbursts, Seyfert galaxies, and infrared luminous galaxies obtained with the PACS spectrometer on board Herschel. We show that the ratio between the far-infrared luminosity and the molecular gas mass, L /M , is a much better proxy for the relative brightness of the far-infrared lines than L alone. Galaxies with high L /M ratios tend to have weaker fine structure lines relative to their far-infrared continuum than galaxies with L /M ≲ 80 L M . A deficit of the [C II] 158 μm line relative to L was previously found with the Infrared Space Observatory, but now we show for the first time that this is a general aspect of all far-infrared fine structure lines, regardless of their origin in the ionized or neutral phase of the interstellar medium. The L /M value where these line deficits start to manifest is similar to the limit that separates between the two modes of star formation recently found in galaxies on the basis of studies of their gas-star formation relations. Our finding that the properties of the interstellar medium are also significantly different in these regimes provides independent support for the different star-forming relations in normal disk galaxies and major merger systems. We use the spectral synthesis code Cloudy to model the emission of the lines. The expected increase of the ionization parameter with L /M can simultaneously explain the line deficits in the [C II], [N II], and [O I] lines. © 2011. The American Astronomical Society. All rights reserved. Printed in the U.S.A.
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Far-infrared line deficits in galaxies with extreme LFIR/M H2 ratios

Astrophysical Journal Letters 728:1 PART II (2011)

Authors:

J Graciá-Carpio, E Sturm, S Hailey-Dunsheath, J Fischer, A Contursi, A Poglitsch, R Genzel, E González-Alfonso, A Sternberg, A Verma, N Christopher, R Davies, H Feuchtgruber, JA De Jong, D Lutz, LJ Tacconi

Abstract:

We report initial results from the far-infrared fine structure line observations of a sample of 44 local starbursts, Seyfert galaxies, and infrared luminous galaxies obtained with the PACS spectrometer on board Herschel. We show that the ratio between the far-infrared luminosity and the molecular gas mass, LFIR/MH2, is a much better proxy for the relative brightness of the far-infrared lines than LFIR alone. Galaxies with high LFIR/MH2 ratios tend to have weaker fine structure lines relative to their far-infrared continuum than galaxies with LFIR/MH2 ≲ 80 L ⊙ M⊙-1. A deficit of the [C II] 158 μm line relative to LFIR was previously found with the Infrared Space Observatory, but now we show for the first time that this is a general aspect of all far-infrared fine structure lines, regardless of their origin in the ionized or neutral phase of the interstellar medium. The L FIR/MH2 value where these line deficits start to manifest is similar to the limit that separates between the two modes of star formation recently found in galaxies on the basis of studies of their gas-star formation relations. Our finding that the properties of the interstellar medium are also significantly different in these regimes provides independent support for the different star-forming relations in normal disk galaxies and major merger systems. We use the spectral synthesis code Cloudy to model the emission of the lines. The expected increase of the ionization parameter with L FIR/MH2 can simultaneously explain the line deficits in the [C II], [N II], and [O I] lines. © 2011. The American Astronomical Society. All rights reserved. Printed in the U.S.A.
More details from the publisher

Spitzer imaging of Herschel-atlas gravitationally lensed submillimeter sources

Astrophysical Journal Letters 728:1 PART II (2011)

Authors:

R Hopwood, J Wardlow, A Cooray, AA Khostovan, S Kim, M Negrello, E Da Cunha, D Burgarella, I Aretxaga, R Auld, M Baes, E Barton, F Bertoldi, DG Bonfield, R Blundell, S Buttiglione, A Cava, DL Clements, J Cooke, H Dannerbauer, A Dariush, G De Zotti, J Dunlop, L Dunne, S Dye, S Eales, J Fritz, D Frayer, MA Gurwell, DH Hughes, E Ibar, RJ Ivison, MJ Jarvis, G Lagache, L Leeuw, S Maddox, MJ Michałlowski, A Omont, E Pascale, M Pohlen, E Rigby, G Rodighiero, D Scott, S Serjeant, I Smail, DJB Smith, P Temi, MA Thompson, I Valtchanov, P Van Der Werf, A Verma, JD Vieira

Abstract:

We present physical properties of two submillimeter selected gravitationally lensed sources, identified in the Herschel Astrophysical Terahertz Large Area Survey. These submillimeter galaxies (SMGs) have flux densities >100 mJy at 500 μm, but are not visible in existing optical imaging. We fit light profiles to each component of the lensing systems in Spitzer IRAC 3.6 and 4.5 μm data and successfully disentangle the foreground lens from the background source in each case, providing important constraints on the spectral energy distributions (SEDs) of the background SMG at rest-frame optical-near-infrared wavelengths. The SED fits show that these two SMGs have high dust obscuration with AV ∼ 4-5 and star formation rates of ∼ 100 M⊙ yr-1. They have low gas fractions and low dynamical masses compared with 850 μm selected galaxies. © 2011. The American Astronomical Society. All rights reserved. Printed in the U.S.A.
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Green Bank Telescope Zpectrometer CO(1-0) observations of the strongly lensed submillimeter galaxies From the Herschel ATLAS

Astrophysical Journal Letters 726:2 PART II (2011)

Authors:

DT Frayer, AI Harris, AJ Baker, RJ Ivison, I Smail, M Negrello, R Maddalena, I Aretxaga, M Baes, M Birkinshaw, DG Bonfield, D Burgarella, S Buttiglione, A Cava, DL Clements, A Cooray, H Dannerbauer, A Dariush, G De Zotti, JS Dunlop, L Dunne, S Dye, S Eales, J Fritz, J Gonzalez-Nuevo, D Herranz, R Hopwood, DH Hughes, E Ibar, MJ Jarvis, G Lagache, LL Leeuw, M Lopez-Caniego, S Maddox, MJ Michałlowski, A Omont, M Pohlen, E Rigby, G Rodighiero, D Scott, S Serjeant, DJB Smith, AM Swinbank, P Temi, MA Thompson, I Valtchanov, PP Van Der Werf, A Verma

Abstract:

The Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS) has uncovered a population of strongly lensed submillimeter galaxies (SMGs). The Zpectrometer instrument on the Green Bank Telescope (GBT) was used to measure the redshifts and constrain the masses of the cold molecular gas reservoirs for two candidate highredshift lensed sources. We derive CO(1-0) redshifts of z = 3.042 ± 0.001 and z = 2.625 ± 0.001, and measure molecular gas masses of (1-3) ×1010M⊙, corrected for lens amplification and assuming a conversion factor of α = 0.8 M ⊙ (Kkm s-1 pc2)-1. We find typical L(IR)/L'(CO) ratios of 120 ±40 and 140±50L ⊙ (Kkm s-1 pc2)-1, which are consistent with those found for local ultraluminous infrared galaxies (ULIRGs) and other high-redshift SMGs. From analysis of published data, we find no evidence for enhanced L(IR)/L'(CO(1-0)) ratios for the SMG population in comparison to local ULIRGs. The GBT results highlight the power of using the CO lines to derive blind redshifts, which is challenging for the SMGs at optical wavelengths given their high obscuration. © 2011. The American Astronomical Society. All rights reserved. Printed in the U.S.A.
More details from the publisher

Far-infrared line deficits in galaxies with extreme LFIR/M H2 ratios

Astrophysical Journal 728:1 PART II (2011)

Authors:

J Graciá-Carpio, E Sturm, S Hailey-Dunsheath, J Fischer, A Contursi, A Poglitsch, R Genzel, E González-Alfonso, A Sternberg, A Verma, N Christopher, R Davies, H Feuchtgruber, JA De Jong, D Lutz, LJ Tacconi
More details from the publisher
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