---
_id: '17779'
abstract:
- lang: eng
  text: The first generation of stars is thought to have formed in low-mass halos
    with Tvir < 10^4 K where H2 cooling is paramount. However, the efficiency of H2
    formation and cooling in these halos may have been severely limited by feedback
    processes. In this paper we investigate the radiative cooling and collapse of
    halos with virial temperatures Tvir > 10^4 K, i.e., those that can cool in the
    absence of H2 via neutral atomic lines. The evolution of these halos differs from
    their less massive counterparts. Efficient atomic line radiation allows rapid
    cooling to ~8000 K; subsequently the gas can contract nearly isothermally at this
    temperature. In the absence of H2 molecules, the gas would likely settle into
    a locally stable disk, and only disks with unusually low spin would be unstable.
    However, we find that the initial atomic line cooling leaves a large, out-of-equilibrium
    residual free electron fraction. This allows the molecular fraction to build up
    to a universal value of x ≈ 10^-3, almost independently of initial density and
    temperature. We show that this is a nonequilibrium freeze-out value that can be
    understood in terms of timescale arguments. Unlike in less massive halos, H2 formation
    and cooling is largely impervious to feedback from external UV fields, due to
    the high initial densities achieved by atomic cooling. The newly formed molecules
    cool the gas further to ~100 K and allow the gas to fragment on scales of a few
    times 100 M☉. We investigate the importance of various feedback effects such as
    H2 photodissociation from internal UV fields and radiation pressure due to Lyα
    photon trapping, which are likely to regulate the efficiency of star formation.
article_processing_charge: No
article_type: original
author:
- first_name: S. Peng
  full_name: Oh, S. Peng
  last_name: Oh
- first_name: Zoltán
  full_name: Haiman, Zoltán
  id: 7c006e8c-cc0d-11ee-8322-cb904ef76f36
  last_name: Haiman
citation:
  ama: 'Oh SP, Haiman Z. Second‐generation objects in the universe: Radiative cooling
    and collapse of halos with virial temperatures above 10^4 K. <i>The Astrophysical
    Journal</i>. 2002;569(2):558-572. doi:<a href="https://doi.org/10.1086/339393">10.1086/339393</a>'
  apa: 'Oh, S. P., &#38; Haiman, Z. (2002). Second‐generation objects in the universe:
    Radiative cooling and collapse of halos with virial temperatures above 10^4 K.
    <i>The Astrophysical Journal</i>. American Astronomical Society. <a href="https://doi.org/10.1086/339393">https://doi.org/10.1086/339393</a>'
  chicago: 'Oh, S. Peng, and Zoltán Haiman. “Second‐generation Objects in the Universe:
    Radiative Cooling and Collapse of Halos with Virial Temperatures above 10^4 K.”
    <i>The Astrophysical Journal</i>. American Astronomical Society, 2002. <a href="https://doi.org/10.1086/339393">https://doi.org/10.1086/339393</a>.'
  ieee: 'S. P. Oh and Z. Haiman, “Second‐generation objects in the universe: Radiative
    cooling and collapse of halos with virial temperatures above 10^4 K,” <i>The Astrophysical
    Journal</i>, vol. 569, no. 2. American Astronomical Society, pp. 558–572, 2002.'
  ista: 'Oh SP, Haiman Z. 2002. Second‐generation objects in the universe: Radiative
    cooling and collapse of halos with virial temperatures above 10^4 K. The Astrophysical
    Journal. 569(2), 558–572.'
  mla: 'Oh, S. Peng, and Zoltán Haiman. “Second‐generation Objects in the Universe:
    Radiative Cooling and Collapse of Halos with Virial Temperatures above 10^4 K.”
    <i>The Astrophysical Journal</i>, vol. 569, no. 2, American Astronomical Society,
    2002, pp. 558–72, doi:<a href="https://doi.org/10.1086/339393">10.1086/339393</a>.'
  short: S.P. Oh, Z. Haiman, The Astrophysical Journal 569 (2002) 558–572.
date_created: 2024-09-06T10:14:24Z
date_published: 2002-04-20T00:00:00Z
date_updated: 2024-09-30T12:04:29Z
day: '20'
doi: 10.1086/339393
extern: '1'
fulldoi: https://doi.org/10.1086/339393
intvolume: '       569'
issue: '2'
language:
- iso: eng
main_file_link:
- open_access: '1'
  url: https://doi.org/10.1086/339393
month: '04'
oa: 1
oa_version: Published Version
page: 558-572
publication: The Astrophysical Journal
publication_identifier:
  issn:
  - 0004-637X
  - 1538-4357
publication_status: published
publisher: American Astronomical Society
quality_controlled: '1'
scopus_import: '1'
status: public
title: 'Second‐generation objects in the universe: Radiative cooling and collapse
  of halos with virial temperatures above 10^4 K'
type: journal_article
user_id: 317138e5-6ab7-11ef-aa6d-ffef3953e345
volume: 569
year: '2002'
...