The influence of environment on the star formation rates of galaxies

Yasuhiro Hashimoto, Augustus Oemler, Huan Lin, Douglas L. Tucker

Research output: Contribution to journalArticle

168 Citations (Scopus)

Abstract

We have used a sample of 15,749 galaxies taken from the Las Campanas Redshift Survey to investigate the effects of environment on the rate of star formation in galaxies. For each galaxy, we derive a measure of the star formation rate (SFR) based on the strength of the [O II] emission line and a measure of galactic structure based on the central concentration of the galaxy's light, which is used to decouple the effect of "morphology-environment" relation from the SFR. Galactic environment is characterized both by the three-space local density of galaxies and by membership in groups and clusters. The size and homogeneity of this data set allows us to sample, for the first time, the entire range of galactic environments, from the lowest density voids to the richest clusters, in a uniform manner. Thus, we could expand our research from the conventional cluster versus field comparison to a new "general" environmental investigation by decoupling the local galaxy density from the membership in associations. This decoupling is crucial for constraining the physical processes responsible for the observed environmental dependencies of star formation. On the other hand, the use of an automatic measure of galactic structure (concentration index) rather than Hubble type, which is a subjective and star formation-contaminated estimate of galactic morphology, allows us to separate cleanly the morphological component from the SFR-environment relationship. We find that, when a cluster/field comparison is made, cluster galaxies exhibit reduced star formation for the same concentration index. This result supports several previous studies based on Hubble type reporting similar suppression of star formation among cluster galaxies for the same Hubble type. We did not find any qualitatively different responses to environments between early- and late-type spirals, which were also previously reported. On the other hand, a further division of clusters by "richness" reveals a new possible excitation of starbursts in groups and poor clusters. Meanwhile, a more general environmental investigation shows that the star formation rate of galaxies with a given concentration index is sensitive to local galaxy density and shows a continuous correlation with the local density, in such a way that galaxies show higher levels of star formation in lower density environments. Interestingly, this trend is also observed both inside and outside of clusters, implying that physical processes responsible for this correlation might not operate intrinsically in the cluster environment. Furthermore, a more complex facet of the dependence of SFR on local density is also revealed; galaxies with differing levels of star formation appear to respond differently to the local density. Low levels of star formation, corresponding to those expected in normal members of the Hubble sequence, are more sensitive to environment inside than outside of clusters. In contrast, high levels of star formation, identified as "starbursts," are at least as sensitive to local density in the field as in clusters. We conclude that at least two separate processes are responsible for the environmental sensitivity of the SFR and tentatively identify gas removal processes as responsible for the variation with density of the SFR of normal galaxies and galaxy-galaxy interactions as responsible for the prevalence of starbursts in intermediate density environments.

Original languageEnglish
Pages (from-to)589-599
Number of pages11
JournalAstrophysical Journal
Volume499
Issue number2 PART I
DOIs
Publication statusPublished - 1998 Jan 1

Fingerprint

star formation rate
galaxies
star formation
galactic structure
rate
decoupling
interacting galaxies
void
homogeneity
division
voids
flat surfaces

Keywords

  • Galaxies: Clusters: General
  • Galaxies: Evolution
  • Galaxies: Interactions
  • Galaxies: Starburst
  • Galaxies: Stellar content
  • Galaxies: Structure

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

The influence of environment on the star formation rates of galaxies. / Hashimoto, Yasuhiro; Oemler, Augustus; Lin, Huan; Tucker, Douglas L.

In: Astrophysical Journal, Vol. 499, No. 2 PART I, 01.01.1998, p. 589-599.

Research output: Contribution to journalArticle

Hashimoto, Yasuhiro ; Oemler, Augustus ; Lin, Huan ; Tucker, Douglas L. / The influence of environment on the star formation rates of galaxies. In: Astrophysical Journal. 1998 ; Vol. 499, No. 2 PART I. pp. 589-599.
@article{d7eb886396ce42aa8d0fed159d9006e0,
title = "The influence of environment on the star formation rates of galaxies",
abstract = "We have used a sample of 15,749 galaxies taken from the Las Campanas Redshift Survey to investigate the effects of environment on the rate of star formation in galaxies. For each galaxy, we derive a measure of the star formation rate (SFR) based on the strength of the [O II] emission line and a measure of galactic structure based on the central concentration of the galaxy's light, which is used to decouple the effect of {"}morphology-environment{"} relation from the SFR. Galactic environment is characterized both by the three-space local density of galaxies and by membership in groups and clusters. The size and homogeneity of this data set allows us to sample, for the first time, the entire range of galactic environments, from the lowest density voids to the richest clusters, in a uniform manner. Thus, we could expand our research from the conventional cluster versus field comparison to a new {"}general{"} environmental investigation by decoupling the local galaxy density from the membership in associations. This decoupling is crucial for constraining the physical processes responsible for the observed environmental dependencies of star formation. On the other hand, the use of an automatic measure of galactic structure (concentration index) rather than Hubble type, which is a subjective and star formation-contaminated estimate of galactic morphology, allows us to separate cleanly the morphological component from the SFR-environment relationship. We find that, when a cluster/field comparison is made, cluster galaxies exhibit reduced star formation for the same concentration index. This result supports several previous studies based on Hubble type reporting similar suppression of star formation among cluster galaxies for the same Hubble type. We did not find any qualitatively different responses to environments between early- and late-type spirals, which were also previously reported. On the other hand, a further division of clusters by {"}richness{"} reveals a new possible excitation of starbursts in groups and poor clusters. Meanwhile, a more general environmental investigation shows that the star formation rate of galaxies with a given concentration index is sensitive to local galaxy density and shows a continuous correlation with the local density, in such a way that galaxies show higher levels of star formation in lower density environments. Interestingly, this trend is also observed both inside and outside of clusters, implying that physical processes responsible for this correlation might not operate intrinsically in the cluster environment. Furthermore, a more complex facet of the dependence of SFR on local density is also revealed; galaxies with differing levels of star formation appear to respond differently to the local density. Low levels of star formation, corresponding to those expected in normal members of the Hubble sequence, are more sensitive to environment inside than outside of clusters. In contrast, high levels of star formation, identified as {"}starbursts,{"} are at least as sensitive to local density in the field as in clusters. We conclude that at least two separate processes are responsible for the environmental sensitivity of the SFR and tentatively identify gas removal processes as responsible for the variation with density of the SFR of normal galaxies and galaxy-galaxy interactions as responsible for the prevalence of starbursts in intermediate density environments.",
keywords = "Galaxies: Clusters: General, Galaxies: Evolution, Galaxies: Interactions, Galaxies: Starburst, Galaxies: Stellar content, Galaxies: Structure",
author = "Yasuhiro Hashimoto and Augustus Oemler and Huan Lin and Tucker, {Douglas L.}",
year = "1998",
month = "1",
day = "1",
doi = "10.1086/305657",
language = "English",
volume = "499",
pages = "589--599",
journal = "Astrophysical Journal",
issn = "0004-637X",
publisher = "IOP Publishing Ltd.",
number = "2 PART I",

}

TY - JOUR

T1 - The influence of environment on the star formation rates of galaxies

AU - Hashimoto, Yasuhiro

AU - Oemler, Augustus

AU - Lin, Huan

AU - Tucker, Douglas L.

PY - 1998/1/1

Y1 - 1998/1/1

N2 - We have used a sample of 15,749 galaxies taken from the Las Campanas Redshift Survey to investigate the effects of environment on the rate of star formation in galaxies. For each galaxy, we derive a measure of the star formation rate (SFR) based on the strength of the [O II] emission line and a measure of galactic structure based on the central concentration of the galaxy's light, which is used to decouple the effect of "morphology-environment" relation from the SFR. Galactic environment is characterized both by the three-space local density of galaxies and by membership in groups and clusters. The size and homogeneity of this data set allows us to sample, for the first time, the entire range of galactic environments, from the lowest density voids to the richest clusters, in a uniform manner. Thus, we could expand our research from the conventional cluster versus field comparison to a new "general" environmental investigation by decoupling the local galaxy density from the membership in associations. This decoupling is crucial for constraining the physical processes responsible for the observed environmental dependencies of star formation. On the other hand, the use of an automatic measure of galactic structure (concentration index) rather than Hubble type, which is a subjective and star formation-contaminated estimate of galactic morphology, allows us to separate cleanly the morphological component from the SFR-environment relationship. We find that, when a cluster/field comparison is made, cluster galaxies exhibit reduced star formation for the same concentration index. This result supports several previous studies based on Hubble type reporting similar suppression of star formation among cluster galaxies for the same Hubble type. We did not find any qualitatively different responses to environments between early- and late-type spirals, which were also previously reported. On the other hand, a further division of clusters by "richness" reveals a new possible excitation of starbursts in groups and poor clusters. Meanwhile, a more general environmental investigation shows that the star formation rate of galaxies with a given concentration index is sensitive to local galaxy density and shows a continuous correlation with the local density, in such a way that galaxies show higher levels of star formation in lower density environments. Interestingly, this trend is also observed both inside and outside of clusters, implying that physical processes responsible for this correlation might not operate intrinsically in the cluster environment. Furthermore, a more complex facet of the dependence of SFR on local density is also revealed; galaxies with differing levels of star formation appear to respond differently to the local density. Low levels of star formation, corresponding to those expected in normal members of the Hubble sequence, are more sensitive to environment inside than outside of clusters. In contrast, high levels of star formation, identified as "starbursts," are at least as sensitive to local density in the field as in clusters. We conclude that at least two separate processes are responsible for the environmental sensitivity of the SFR and tentatively identify gas removal processes as responsible for the variation with density of the SFR of normal galaxies and galaxy-galaxy interactions as responsible for the prevalence of starbursts in intermediate density environments.

AB - We have used a sample of 15,749 galaxies taken from the Las Campanas Redshift Survey to investigate the effects of environment on the rate of star formation in galaxies. For each galaxy, we derive a measure of the star formation rate (SFR) based on the strength of the [O II] emission line and a measure of galactic structure based on the central concentration of the galaxy's light, which is used to decouple the effect of "morphology-environment" relation from the SFR. Galactic environment is characterized both by the three-space local density of galaxies and by membership in groups and clusters. The size and homogeneity of this data set allows us to sample, for the first time, the entire range of galactic environments, from the lowest density voids to the richest clusters, in a uniform manner. Thus, we could expand our research from the conventional cluster versus field comparison to a new "general" environmental investigation by decoupling the local galaxy density from the membership in associations. This decoupling is crucial for constraining the physical processes responsible for the observed environmental dependencies of star formation. On the other hand, the use of an automatic measure of galactic structure (concentration index) rather than Hubble type, which is a subjective and star formation-contaminated estimate of galactic morphology, allows us to separate cleanly the morphological component from the SFR-environment relationship. We find that, when a cluster/field comparison is made, cluster galaxies exhibit reduced star formation for the same concentration index. This result supports several previous studies based on Hubble type reporting similar suppression of star formation among cluster galaxies for the same Hubble type. We did not find any qualitatively different responses to environments between early- and late-type spirals, which were also previously reported. On the other hand, a further division of clusters by "richness" reveals a new possible excitation of starbursts in groups and poor clusters. Meanwhile, a more general environmental investigation shows that the star formation rate of galaxies with a given concentration index is sensitive to local galaxy density and shows a continuous correlation with the local density, in such a way that galaxies show higher levels of star formation in lower density environments. Interestingly, this trend is also observed both inside and outside of clusters, implying that physical processes responsible for this correlation might not operate intrinsically in the cluster environment. Furthermore, a more complex facet of the dependence of SFR on local density is also revealed; galaxies with differing levels of star formation appear to respond differently to the local density. Low levels of star formation, corresponding to those expected in normal members of the Hubble sequence, are more sensitive to environment inside than outside of clusters. In contrast, high levels of star formation, identified as "starbursts," are at least as sensitive to local density in the field as in clusters. We conclude that at least two separate processes are responsible for the environmental sensitivity of the SFR and tentatively identify gas removal processes as responsible for the variation with density of the SFR of normal galaxies and galaxy-galaxy interactions as responsible for the prevalence of starbursts in intermediate density environments.

KW - Galaxies: Clusters: General

KW - Galaxies: Evolution

KW - Galaxies: Interactions

KW - Galaxies: Starburst

KW - Galaxies: Stellar content

KW - Galaxies: Structure

UR - http://www.scopus.com/inward/record.url?scp=22044438179&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=22044438179&partnerID=8YFLogxK

U2 - 10.1086/305657

DO - 10.1086/305657

M3 - Article

AN - SCOPUS:22044438179

VL - 499

SP - 589

EP - 599

JO - Astrophysical Journal

JF - Astrophysical Journal

SN - 0004-637X

IS - 2 PART I

ER -