Ultraviolet spectroscopy of the quasar pair LB 9605, LB 9612 with the Hubble Space Telescope

Evolution in the size of the Lyα absorbers?

Nadine Dinshaw, Craig B. Foltz, Christopher D Impey, Ray J. Weymann

Research output: Contribution to journalArticle

29 Citations (Scopus)

Abstract

Ultraviolet spectroscopy has been obtained with the faint object spectrograph of the Hubble Space Telescope in the Lyα forest of the quasar pair, LB 9605 (zem = 1.834) and LB 9612 (zem = 1.898), in order to measure the size of the Lyα absorbers. The quasars are separated by 1′.65 on the sky corresponding to a proper separation of 412 h-1 kpc at z = 1.83 (where h ≡ H0/100 km s-1 Mpc-1; q0 = 0.5). We detect five Lyα absorption lines common to both spectra within a velocity difference of 400 km s-1 in the redshift range 1.06 < z < 1.69, and 20 lines which are seen in the spectrum of one quasar but not the other. The number of coincidences expected for randomly distributed absorbers in this redshift interval is 3.2 ± 1.8, implying a less than 2 σ significance for the observed coincidences. If none of the observed coincidences are real, then we can place an upper limit on the absorber radius with 95% confidence of ∼285 h-1 kpc for redshifts 1.06 < z < 1.69. If, on the other hand, all of the observed coincidences are real, then a maximum likelihood estimate of the characteristic absorber radius in the context of identical, spherical clouds give a most probable radius of 380 h-1 kpc with 95% confidence that the characteristic radius lies in the range 305 < R < 595 h-1 kpc. Taken together with a low redshift estimate and new ground-based estimates, the upper limit on the absorber size provides tantalizing evidence for evolution in the radius of the Lyα absorbers with cosmic time, in the sense that the characteristic size of the Lyα absorbers increases with decreasing redshift.

Original languageEnglish (US)
Pages (from-to)567-580
Number of pages14
JournalAstrophysical Journal
Volume494
Issue number2 PART I
DOIs
StatePublished - 1998

Fingerprint

ultraviolet spectroscopy
Hubble Space Telescope
quasars
absorbers
spectroscopy
radii
confidence
maximum likelihood estimates
faint objects
estimates
spectrographs
sky
intervals

Keywords

  • Intergalactic medium
  • Quasars: absorption lines
  • Quasars: individual (LB 9605, LB 9612)
  • Ultraviolet: galaxies

ASJC Scopus subject areas

  • Space and Planetary Science

Cite this

Ultraviolet spectroscopy of the quasar pair LB 9605, LB 9612 with the Hubble Space Telescope : Evolution in the size of the Lyα absorbers? / Dinshaw, Nadine; Foltz, Craig B.; Impey, Christopher D; Weymann, Ray J.

In: Astrophysical Journal, Vol. 494, No. 2 PART I, 1998, p. 567-580.

Research output: Contribution to journalArticle

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title = "Ultraviolet spectroscopy of the quasar pair LB 9605, LB 9612 with the Hubble Space Telescope: Evolution in the size of the Lyα absorbers?",
abstract = "Ultraviolet spectroscopy has been obtained with the faint object spectrograph of the Hubble Space Telescope in the Lyα forest of the quasar pair, LB 9605 (zem = 1.834) and LB 9612 (zem = 1.898), in order to measure the size of the Lyα absorbers. The quasars are separated by 1′.65 on the sky corresponding to a proper separation of 412 h-1 kpc at z = 1.83 (where h ≡ H0/100 km s-1 Mpc-1; q0 = 0.5). We detect five Lyα absorption lines common to both spectra within a velocity difference of 400 km s-1 in the redshift range 1.06 < z < 1.69, and 20 lines which are seen in the spectrum of one quasar but not the other. The number of coincidences expected for randomly distributed absorbers in this redshift interval is 3.2 ± 1.8, implying a less than 2 σ significance for the observed coincidences. If none of the observed coincidences are real, then we can place an upper limit on the absorber radius with 95{\%} confidence of ∼285 h-1 kpc for redshifts 1.06 < z < 1.69. If, on the other hand, all of the observed coincidences are real, then a maximum likelihood estimate of the characteristic absorber radius in the context of identical, spherical clouds give a most probable radius of 380 h-1 kpc with 95{\%} confidence that the characteristic radius lies in the range 305 < R < 595 h-1 kpc. Taken together with a low redshift estimate and new ground-based estimates, the upper limit on the absorber size provides tantalizing evidence for evolution in the radius of the Lyα absorbers with cosmic time, in the sense that the characteristic size of the Lyα absorbers increases with decreasing redshift.",
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T1 - Ultraviolet spectroscopy of the quasar pair LB 9605, LB 9612 with the Hubble Space Telescope

T2 - Evolution in the size of the Lyα absorbers?

AU - Dinshaw, Nadine

AU - Foltz, Craig B.

AU - Impey, Christopher D

AU - Weymann, Ray J.

PY - 1998

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N2 - Ultraviolet spectroscopy has been obtained with the faint object spectrograph of the Hubble Space Telescope in the Lyα forest of the quasar pair, LB 9605 (zem = 1.834) and LB 9612 (zem = 1.898), in order to measure the size of the Lyα absorbers. The quasars are separated by 1′.65 on the sky corresponding to a proper separation of 412 h-1 kpc at z = 1.83 (where h ≡ H0/100 km s-1 Mpc-1; q0 = 0.5). We detect five Lyα absorption lines common to both spectra within a velocity difference of 400 km s-1 in the redshift range 1.06 < z < 1.69, and 20 lines which are seen in the spectrum of one quasar but not the other. The number of coincidences expected for randomly distributed absorbers in this redshift interval is 3.2 ± 1.8, implying a less than 2 σ significance for the observed coincidences. If none of the observed coincidences are real, then we can place an upper limit on the absorber radius with 95% confidence of ∼285 h-1 kpc for redshifts 1.06 < z < 1.69. If, on the other hand, all of the observed coincidences are real, then a maximum likelihood estimate of the characteristic absorber radius in the context of identical, spherical clouds give a most probable radius of 380 h-1 kpc with 95% confidence that the characteristic radius lies in the range 305 < R < 595 h-1 kpc. Taken together with a low redshift estimate and new ground-based estimates, the upper limit on the absorber size provides tantalizing evidence for evolution in the radius of the Lyα absorbers with cosmic time, in the sense that the characteristic size of the Lyα absorbers increases with decreasing redshift.

AB - Ultraviolet spectroscopy has been obtained with the faint object spectrograph of the Hubble Space Telescope in the Lyα forest of the quasar pair, LB 9605 (zem = 1.834) and LB 9612 (zem = 1.898), in order to measure the size of the Lyα absorbers. The quasars are separated by 1′.65 on the sky corresponding to a proper separation of 412 h-1 kpc at z = 1.83 (where h ≡ H0/100 km s-1 Mpc-1; q0 = 0.5). We detect five Lyα absorption lines common to both spectra within a velocity difference of 400 km s-1 in the redshift range 1.06 < z < 1.69, and 20 lines which are seen in the spectrum of one quasar but not the other. The number of coincidences expected for randomly distributed absorbers in this redshift interval is 3.2 ± 1.8, implying a less than 2 σ significance for the observed coincidences. If none of the observed coincidences are real, then we can place an upper limit on the absorber radius with 95% confidence of ∼285 h-1 kpc for redshifts 1.06 < z < 1.69. If, on the other hand, all of the observed coincidences are real, then a maximum likelihood estimate of the characteristic absorber radius in the context of identical, spherical clouds give a most probable radius of 380 h-1 kpc with 95% confidence that the characteristic radius lies in the range 305 < R < 595 h-1 kpc. Taken together with a low redshift estimate and new ground-based estimates, the upper limit on the absorber size provides tantalizing evidence for evolution in the radius of the Lyα absorbers with cosmic time, in the sense that the characteristic size of the Lyα absorbers increases with decreasing redshift.

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