X-ray properties of Lyman break galaxies in the Hubble Deep Field-North region

K. Nandra, R. F. Mushotzky, K. Arnaud, C. C. Steidel, K. L. Adelberger, J. P. Gardner, H. I. Teplitz, Rogier Windhorst

Research output: Contribution to journalArticle

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Abstract

We describe the X-ray properties of a large sample of z ∼ 3 Lyman break galaxies (LBGs) in the region of the Hubble Deep Field-North, derived from the 1 Ms public Chandra observation. Of our sample of 148 LBGs, four are detected individually. This immediately gives a measure of the bright AGN fraction in these galaxies of ∼3%, which is in agreement with that derived from the UV spectra. The X-ray color of the detected sources indicates that they are probably moderately obscured. Stacking of the remainder shows a significant detection (6 σ) with an average luminosity of 3.4 × 1041 ergs s-1 per galaxy in the rest-frame 2-10 keV band. We have also studied a comparison sample of 95 z ∼ 1 "Balmer break" galaxies. Eight of these are detected directly, with at least two clear AGNs based on their high X-ray luminosity and very hard X-ray spectra. The remainder are of relatively low luminosity (<1042 ergs s -1), and the X-rays could arise from either AGNs or rapid star formation. The X-ray colors and evidence from other wave bands favor the latter interpretation. Excluding the clear AGNs, we deduce a mean X-ray luminosity of 6.6 × 1040 ergs s-1, a factor of ∼5 lower than the LBGs. The average ratio of the UV and X-ray luminosities of these star-forming galaxies LUV/LX, however, is approximately the same at z = 1 as it is at z = 3. This scaling implies that the X-ray emission follows the current star formation rate, as measured by the UV luminosity. We use our results to constrain the star formation rate at z ∼ 3 from an X-ray perspective. Assuming the locally established correlation between X-ray and far-IR luminosity, the average inferred star formation rate in each LBG is found to be approximately 60 M yr-1, in excellent agreement with the extinction-corrected UV estimates. This provides an external check on the UV estimates of the star formation rates and on the use of X-ray luminosities to infer these rates in rapidly star-forming galaxies at high redshift.

Original languageEnglish (US)
Pages (from-to)625-639
Number of pages15
JournalAstrophysical Journal
Volume576
Issue number2 I
DOIs
StatePublished - Sep 10 2002

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galaxies
luminosity
x rays
star formation rate
erg
color
stars
estimates
stacking
star formation
extinction
rate
scaling

Keywords

  • Galaxies: active
  • Galaxies: evolution
  • Galaxies: high-redshift
  • Galaxies: nuclei
  • X-rays: galaxies

ASJC Scopus subject areas

  • Space and Planetary Science

Cite this

Nandra, K., Mushotzky, R. F., Arnaud, K., Steidel, C. C., Adelberger, K. L., Gardner, J. P., ... Windhorst, R. (2002). X-ray properties of Lyman break galaxies in the Hubble Deep Field-North region. Astrophysical Journal, 576(2 I), 625-639. https://doi.org/10.1086/341888

X-ray properties of Lyman break galaxies in the Hubble Deep Field-North region. / Nandra, K.; Mushotzky, R. F.; Arnaud, K.; Steidel, C. C.; Adelberger, K. L.; Gardner, J. P.; Teplitz, H. I.; Windhorst, Rogier.

In: Astrophysical Journal, Vol. 576, No. 2 I, 10.09.2002, p. 625-639.

Research output: Contribution to journalArticle

Nandra, K, Mushotzky, RF, Arnaud, K, Steidel, CC, Adelberger, KL, Gardner, JP, Teplitz, HI & Windhorst, R 2002, 'X-ray properties of Lyman break galaxies in the Hubble Deep Field-North region', Astrophysical Journal, vol. 576, no. 2 I, pp. 625-639. https://doi.org/10.1086/341888
Nandra K, Mushotzky RF, Arnaud K, Steidel CC, Adelberger KL, Gardner JP et al. X-ray properties of Lyman break galaxies in the Hubble Deep Field-North region. Astrophysical Journal. 2002 Sep 10;576(2 I):625-639. https://doi.org/10.1086/341888
Nandra, K. ; Mushotzky, R. F. ; Arnaud, K. ; Steidel, C. C. ; Adelberger, K. L. ; Gardner, J. P. ; Teplitz, H. I. ; Windhorst, Rogier. / X-ray properties of Lyman break galaxies in the Hubble Deep Field-North region. In: Astrophysical Journal. 2002 ; Vol. 576, No. 2 I. pp. 625-639.
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AU - Arnaud, K.

AU - Steidel, C. C.

AU - Adelberger, K. L.

AU - Gardner, J. P.

AU - Teplitz, H. I.

AU - Windhorst, Rogier

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N2 - We describe the X-ray properties of a large sample of z ∼ 3 Lyman break galaxies (LBGs) in the region of the Hubble Deep Field-North, derived from the 1 Ms public Chandra observation. Of our sample of 148 LBGs, four are detected individually. This immediately gives a measure of the bright AGN fraction in these galaxies of ∼3%, which is in agreement with that derived from the UV spectra. The X-ray color of the detected sources indicates that they are probably moderately obscured. Stacking of the remainder shows a significant detection (6 σ) with an average luminosity of 3.4 × 1041 ergs s-1 per galaxy in the rest-frame 2-10 keV band. We have also studied a comparison sample of 95 z ∼ 1 "Balmer break" galaxies. Eight of these are detected directly, with at least two clear AGNs based on their high X-ray luminosity and very hard X-ray spectra. The remainder are of relatively low luminosity (<1042 ergs s -1), and the X-rays could arise from either AGNs or rapid star formation. The X-ray colors and evidence from other wave bands favor the latter interpretation. Excluding the clear AGNs, we deduce a mean X-ray luminosity of 6.6 × 1040 ergs s-1, a factor of ∼5 lower than the LBGs. The average ratio of the UV and X-ray luminosities of these star-forming galaxies LUV/LX, however, is approximately the same at z = 1 as it is at z = 3. This scaling implies that the X-ray emission follows the current star formation rate, as measured by the UV luminosity. We use our results to constrain the star formation rate at z ∼ 3 from an X-ray perspective. Assuming the locally established correlation between X-ray and far-IR luminosity, the average inferred star formation rate in each LBG is found to be approximately 60 M⊙ yr-1, in excellent agreement with the extinction-corrected UV estimates. This provides an external check on the UV estimates of the star formation rates and on the use of X-ray luminosities to infer these rates in rapidly star-forming galaxies at high redshift.

AB - We describe the X-ray properties of a large sample of z ∼ 3 Lyman break galaxies (LBGs) in the region of the Hubble Deep Field-North, derived from the 1 Ms public Chandra observation. Of our sample of 148 LBGs, four are detected individually. This immediately gives a measure of the bright AGN fraction in these galaxies of ∼3%, which is in agreement with that derived from the UV spectra. The X-ray color of the detected sources indicates that they are probably moderately obscured. Stacking of the remainder shows a significant detection (6 σ) with an average luminosity of 3.4 × 1041 ergs s-1 per galaxy in the rest-frame 2-10 keV band. We have also studied a comparison sample of 95 z ∼ 1 "Balmer break" galaxies. Eight of these are detected directly, with at least two clear AGNs based on their high X-ray luminosity and very hard X-ray spectra. The remainder are of relatively low luminosity (<1042 ergs s -1), and the X-rays could arise from either AGNs or rapid star formation. The X-ray colors and evidence from other wave bands favor the latter interpretation. Excluding the clear AGNs, we deduce a mean X-ray luminosity of 6.6 × 1040 ergs s-1, a factor of ∼5 lower than the LBGs. The average ratio of the UV and X-ray luminosities of these star-forming galaxies LUV/LX, however, is approximately the same at z = 1 as it is at z = 3. This scaling implies that the X-ray emission follows the current star formation rate, as measured by the UV luminosity. We use our results to constrain the star formation rate at z ∼ 3 from an X-ray perspective. Assuming the locally established correlation between X-ray and far-IR luminosity, the average inferred star formation rate in each LBG is found to be approximately 60 M⊙ yr-1, in excellent agreement with the extinction-corrected UV estimates. This provides an external check on the UV estimates of the star formation rates and on the use of X-ray luminosities to infer these rates in rapidly star-forming galaxies at high redshift.

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KW - Galaxies: evolution

KW - Galaxies: high-redshift

KW - Galaxies: nuclei

KW - X-rays: galaxies

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