Origin of Lyα absorption in nearby starbursts and implications for other galaxies

被引:25
作者
Atek, H. [1 ]
Schaerer, D. [2 ,3 ]
Kunth, D. [1 ]
机构
[1] Inst Astrophys, F-75014 Paris, France
[2] Univ Geneva, Observ Geneva, CH-1290 Sauverny, Switzerland
[3] Univ Toulouse, CNRS, Lab Astrophys Toulouse Tarbes, F-31400 Toulouse, France
基金
瑞士国家科学基金会;
关键词
galaxies: starburst; galaxies: ISM; ultraviolet: galaxies; radiative transfer; galaxies: individual: IZw 18; STAR-FORMING GALAXIES; I ZW 18; LYMAN-BREAK GALAXIES; SUBARU DEEP FIELD; COMPACT DWARF GALAXIES; WOLF-RAYET STARS; SIMILAR-TO; HIGH-REDSHIFT; RADIATION TRANSFER; YOUNG GALAXIES;
D O I
10.1051/0004-6361/200911856
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
Context. Despite the privileged position that Lyman-alpha (Ly alpha) emission line holds in the exploration of the distant universe and modern observational cosmology, the origin of the observed diversity of Ly alpha profiles still needs to be thoroughly explained. Observations of nearby star forming galaxies bring their batch of apparent contradictions between Ly alpha emission and their physical parameters, and call for a detailed understanding of the physical processes at work. One of the most metal-poor galaxies known, IZw 18, is of particular interest in this context. Aims. We fit the Ly alpha spectrum of IZw 18 to understand the origin of the damped absorption profile and its spatial variations across the NW region, and establish a general picture of the physical parameters governing the Ly alpha strength and profile both in local and in high-z galaxies. Methods. We used a 3D Ly alpha radiation transfer code to model Hubble Space Telescope (HST) observations of IZw 18. Observational constraints of relevant parameters such as dust or HI column density were derived from previous studies and from the present analysis. Different geometrical configurations of the source and the neutral gas were explored. Results. The integrated Ly alpha profile of NWregion of IZw 18 is reproduced using the observed small amount of dust (E(B-V) approximate to 0.05) and a spherical HI shell with N(HI) = 6.5 x 10(21) cm(-2). Such a high column density makes it possible to transform a strong Ly alpha emission (EW(Ly alpha) = 60 angstrom) into a damped absorption even with low extinction. When a slab geometry is applied and a given line of sight is chosen, the Ly alpha profile can be successfully reproduced with no dust at all and N(HI) = 3 x 10(21) cm(-2). The spatial variations of the profile shape are naturally explained by radiation transfer effects, i.e. by scattering of Ly alpha photons, when the observed surface brightness profile of the source is taken into account. In the case of outflowing inter stellar medium (ISM), as commonly observed in Lyman break galaxies (LBGs), a high N(HI) and dust content are required to observe Lya in absorption. For nearly static neutral gas as observed in IZw 18 and other low-luminosity galaxies, only a small amount of dust is required provided a sufficiently high N(HI) covers the galaxy. We also show how geometrical and apertures effects affect the Ly alpha profile.
引用
收藏
页码:791 / 801
页数:11
相关论文
共 78 条
[1]   A Subaru search for Lyα emitters at redshift 5.7 [J].
Ajiki, M ;
Taniguchi, Y ;
Fujita, SS ;
Shioya, Y ;
Nagao, T ;
Murayama, T ;
Yamada, S ;
Umeda, K ;
Komiyama, Y .
ASTRONOMICAL JOURNAL, 2003, 126 (05) :2091-2107
[2]   On the detectability of Lyα emission in star forming galaxies -: The role of dust [J].
Atek, H. ;
Kunth, D. ;
Hayes, M. ;
Oestlin, G. ;
Mas-Hesse, J. M. .
ASTRONOMY & ASTROPHYSICS, 2008, 488 (02) :491-509
[3]  
ATEK H, 2009, A A UNPUB
[4]   HI and CO in blue compact dwarf galaxies: Haro 2 and Haro 4 [J].
Bravo-Alfaro, H ;
Brinks, E ;
Baker, AJ ;
Walter, F ;
Kunth, D .
ASTRONOMICAL JOURNAL, 2004, 127 (01) :264-278
[6]   Isolating clusters with Wolf-Rayet stars in I Zw 18 (vol 579, pg L75, 2002) [J].
Brown, TM ;
Heap, SR ;
Hubeny, I ;
Lanz, T ;
Lindler, D .
ASTROPHYSICAL JOURNAL, 2002, 581 (02) :L129-L129
[7]   Medium-resolution spectroscopy of FORJ0332-3557:: probing the interstellar medium and stellar populations of a lensed Lyman-break galaxy at z=3.77 [J].
Cabanac, Remi A. ;
Valls-Gabaud, David ;
Lidman, Chris .
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 2008, 386 (04) :2065-2074
[8]   Dust in I Zw 18 from Hubble Space Telescope narrowband imaging [J].
Cannon, JM ;
Skillman, ED ;
Garnett, DR ;
Dufour, RJ .
ASTROPHYSICAL JOURNAL, 2002, 565 (02) :931-940
[9]   THE RELATIONSHIP BETWEEN INFRARED, OPTICAL, AND ULTRAVIOLET EXTINCTION [J].
CARDELLI, JA ;
CLAYTON, GC ;
MATHIS, JS .
ASTROPHYSICAL JOURNAL, 1989, 345 (01) :245-256
[10]   LYMAN-ALPHA EMISSION FROM GALAXIES [J].
CHARLOT, S ;
FALL, SM .
ASTROPHYSICAL JOURNAL, 1993, 415 (02) :580-588