### Abstract

We present further analysis and discussion of the properties of the absorption lines in the QSO pair Q0107-025A,B (z_{em} = 0.956, 0.952; angular separation 1′.129) based upon spectroscopy obtained with the Faint Object Spectrograph (FOS) of the Hubble Space Telescope (HST). We also present observations of the pair at shorter wavelengths taken with the HST Goddard High Resolution Spectrograph lowresolution grating, as well as Multiple Mirror Telescope spectra obtained with the intent of looking for metal-line counterparts to the Lyman-α absorption systems. The most interesting feature revealed by the GHRS spectra is a weak Lyman limit system with a redshift of Z_{LLS} = 0.3997. The Lyman limit system itself is seen only in Q0107-025B, but corresponding Lyα lines can be seen in the FOS spectra of both Q0107-025A and B indicating that lower column density gas extends out to greater distances than higher column density gas. From a sample of 5 σ lines with W_{0} > 0.32 Å detected in the FOS spectra, we count five systems (including a probable system) common to both spectra with velocity differences less than 150 km s^{-1}, and six systems that are not in common to both spectra in the redshift range 0.48 < z < 0.89. From the presence of common absorption, we obtain lower limits on the radius of the absorbers of 140-160 h^{-1} kpc [h = H_{0}/(100 km s^{-1} Mpc^{-1}); q_{0} = 0.5]. Using a simple maximum-likelihood analysis, we estimate a characteristic radius of 505 h^{-1} kpc assuming spherical absorbers, with 95% confidence lower and upper limits of 345 < R < 1520 h^{-1} kpc. For disklike absorbers, we derive a most probable radius of 715 h^{-1} kpc and 95% confidence limits of 470 < R < 2310 h^{-1} kpc. We also present a new statistical technique to test the relative likelihood of three geometric models. In particular, we consider spherical absorbers, with and without a distribution in size, as well as filamentary and disklike absorbers. Spherical absorbers with uniform radius can be ruled out since they cannot simultaneously reproduce the large equivalent width coincidences and anticoincidences observed. The model that best reproduce the equivalent width distribution of the observed coincident and anticoincident systems corresponds to randomly inclined disks with characteristic radius 915 h^{-1} kpc and 95% confidence interval 560 < R < 1270 h^{-1} kpc. Our results are in agreement with recent cosmological simulations that produce Lyα forest absorbers in the form of filaments and sheets with coherence lengths as great as 1 Mpc.

Original language | English (US) |
---|---|

Pages (from-to) | 45-68 |

Number of pages | 24 |

Journal | Astrophysical Journal |

Volume | 491 |

Issue number | 1 PART I |

DOIs | |

State | Published - 1997 |

Externally published | Yes |

### Fingerprint

### Keywords

- Galaxies: clusters: general
- Intergalactic medium
- Quasars: absorption lines quasars: individual (Q0107-025A,B)

### ASJC Scopus subject areas

- Space and Planetary Science

### Cite this

*Astrophysical Journal*,

*491*(1 PART I), 45-68. https://doi.org/10.1086/304926

**Additional observations and analysis of the Lyman-α absorption lines toward the QSO Pair Q0107-025A 1,2.** / Dinshaw, Nadine; Weymann, Ray J.; Impey, Christopher D; Foltz, Craig B.; Morris, Simon L.; Ake, Tom.

Research output: Contribution to journal › Article

*Astrophysical Journal*, vol. 491, no. 1 PART I, pp. 45-68. https://doi.org/10.1086/304926

}

TY - JOUR

T1 - Additional observations and analysis of the Lyman-α absorption lines toward the QSO Pair Q0107-025A 1,2

AU - Dinshaw, Nadine

AU - Weymann, Ray J.

AU - Impey, Christopher D

AU - Foltz, Craig B.

AU - Morris, Simon L.

AU - Ake, Tom

PY - 1997

Y1 - 1997

N2 - We present further analysis and discussion of the properties of the absorption lines in the QSO pair Q0107-025A,B (zem = 0.956, 0.952; angular separation 1′.129) based upon spectroscopy obtained with the Faint Object Spectrograph (FOS) of the Hubble Space Telescope (HST). We also present observations of the pair at shorter wavelengths taken with the HST Goddard High Resolution Spectrograph lowresolution grating, as well as Multiple Mirror Telescope spectra obtained with the intent of looking for metal-line counterparts to the Lyman-α absorption systems. The most interesting feature revealed by the GHRS spectra is a weak Lyman limit system with a redshift of ZLLS = 0.3997. The Lyman limit system itself is seen only in Q0107-025B, but corresponding Lyα lines can be seen in the FOS spectra of both Q0107-025A and B indicating that lower column density gas extends out to greater distances than higher column density gas. From a sample of 5 σ lines with W0 > 0.32 Å detected in the FOS spectra, we count five systems (including a probable system) common to both spectra with velocity differences less than 150 km s-1, and six systems that are not in common to both spectra in the redshift range 0.48 < z < 0.89. From the presence of common absorption, we obtain lower limits on the radius of the absorbers of 140-160 h-1 kpc [h = H0/(100 km s-1 Mpc-1); q0 = 0.5]. Using a simple maximum-likelihood analysis, we estimate a characteristic radius of 505 h-1 kpc assuming spherical absorbers, with 95% confidence lower and upper limits of 345 < R < 1520 h-1 kpc. For disklike absorbers, we derive a most probable radius of 715 h-1 kpc and 95% confidence limits of 470 < R < 2310 h-1 kpc. We also present a new statistical technique to test the relative likelihood of three geometric models. In particular, we consider spherical absorbers, with and without a distribution in size, as well as filamentary and disklike absorbers. Spherical absorbers with uniform radius can be ruled out since they cannot simultaneously reproduce the large equivalent width coincidences and anticoincidences observed. The model that best reproduce the equivalent width distribution of the observed coincident and anticoincident systems corresponds to randomly inclined disks with characteristic radius 915 h-1 kpc and 95% confidence interval 560 < R < 1270 h-1 kpc. Our results are in agreement with recent cosmological simulations that produce Lyα forest absorbers in the form of filaments and sheets with coherence lengths as great as 1 Mpc.

AB - We present further analysis and discussion of the properties of the absorption lines in the QSO pair Q0107-025A,B (zem = 0.956, 0.952; angular separation 1′.129) based upon spectroscopy obtained with the Faint Object Spectrograph (FOS) of the Hubble Space Telescope (HST). We also present observations of the pair at shorter wavelengths taken with the HST Goddard High Resolution Spectrograph lowresolution grating, as well as Multiple Mirror Telescope spectra obtained with the intent of looking for metal-line counterparts to the Lyman-α absorption systems. The most interesting feature revealed by the GHRS spectra is a weak Lyman limit system with a redshift of ZLLS = 0.3997. The Lyman limit system itself is seen only in Q0107-025B, but corresponding Lyα lines can be seen in the FOS spectra of both Q0107-025A and B indicating that lower column density gas extends out to greater distances than higher column density gas. From a sample of 5 σ lines with W0 > 0.32 Å detected in the FOS spectra, we count five systems (including a probable system) common to both spectra with velocity differences less than 150 km s-1, and six systems that are not in common to both spectra in the redshift range 0.48 < z < 0.89. From the presence of common absorption, we obtain lower limits on the radius of the absorbers of 140-160 h-1 kpc [h = H0/(100 km s-1 Mpc-1); q0 = 0.5]. Using a simple maximum-likelihood analysis, we estimate a characteristic radius of 505 h-1 kpc assuming spherical absorbers, with 95% confidence lower and upper limits of 345 < R < 1520 h-1 kpc. For disklike absorbers, we derive a most probable radius of 715 h-1 kpc and 95% confidence limits of 470 < R < 2310 h-1 kpc. We also present a new statistical technique to test the relative likelihood of three geometric models. In particular, we consider spherical absorbers, with and without a distribution in size, as well as filamentary and disklike absorbers. Spherical absorbers with uniform radius can be ruled out since they cannot simultaneously reproduce the large equivalent width coincidences and anticoincidences observed. The model that best reproduce the equivalent width distribution of the observed coincident and anticoincident systems corresponds to randomly inclined disks with characteristic radius 915 h-1 kpc and 95% confidence interval 560 < R < 1270 h-1 kpc. Our results are in agreement with recent cosmological simulations that produce Lyα forest absorbers in the form of filaments and sheets with coherence lengths as great as 1 Mpc.

KW - Galaxies: clusters: general

KW - Intergalactic medium

KW - Quasars: absorption lines quasars: individual (Q0107-025A,B)

UR - http://www.scopus.com/inward/record.url?scp=0039292737&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0039292737&partnerID=8YFLogxK

U2 - 10.1086/304926

DO - 10.1086/304926

M3 - Article

VL - 491

SP - 45

EP - 68

JO - Astrophysical Journal

JF - Astrophysical Journal

SN - 0004-637X

IS - 1 PART I

ER -