This study presents a comprehensive multi-wavelength analysis of five poststarburst galaxies with stellar masses greater than $10^{11} M_\odot$ at a redshift of approximately 0.7. The authors examine the stars, gas, and current and past star-formation activities in these galaxies. Using optical images from the Subaru telescope and Hubble Space Telescope, the authors observe a high incidence of companion galaxies and low surface brightness tidal features, indicating that quenching (the process by which galaxies cease their star formation) is closely related to interactions between galaxies. The authors also analyze optical spectra provided by the LEGA-C survey to model the stellar continuum and derive the star-formation histories of these poststarburst galaxies. They find that the progenitors of these galaxies had stellar masses ranging from $2\times10^9 M_\odot$ to $10^{11} M_\odot$ and underwent a burst of star formation several hundred million years prior to observation, with a decay time scale of approximately 100 million years. Additionally, ALMA observations detect CO(2-1) emission in four out of the five galaxies studied. The molecular gas is found to spread over distances greater than 1 arcsecond (equivalent to approximately 10 kiloparsecs) with a mass reaching up to approximately $2 \times10^{10} M_\odot$. However, despite detecting molecular gas, the authors find that star-forming regions within these galaxies are unresolved by both slit spectra and 3 GHz continuum observations conducted by the Very Large Array. Comparisons between star-formation rates and gas masses as well as sizes of CO emission and star-forming regions suggest a low star-forming efficiency in these poststarburst galaxies. The authors demonstrate that commonly used calibrations based on infrared and radio luminosities tend to overestimate true values due to radiation from old stars and contributions from active galactic nuclei (AGN). Weak AGN-driven outflows are revealed by the optical spectra. In conclusion, this study provides valuable insights into the properties and evolution of poststarburst galaxies with high stellar masses. The findings highlight the importance of galaxy interactions in quenching star formation and emphasize the need for accurate measurements of star-formation rates in order to understand the true nature of these galaxies.
- Study focuses on five poststarburst galaxies with stellar masses > $10^{11} M_\odot$ at redshift ~0.7
- High incidence of companion galaxies and low surface brightness tidal features indicate quenching is related to galaxy interactions
- Progenitors of these galaxies had stellar masses ranging from $2\times10^9 M_\odot$ to $10^{11} M_\odot$
- Burst of star formation occurred several hundred million years prior to observation, with decay time scale of ~100 million years
- ALMA observations detect CO(2-1) emission in four out of the five galaxies studied
- Molecular gas spreads over distances > 1 arcsecond (~10 kiloparsecs) with mass up to ~$2 \times10^{10} M_\odot$
- Star-forming regions within these galaxies are unresolved by slit spectra and 3 GHz continuum observations
- Comparisons suggest low star-forming efficiency in these poststarburst galaxies
- Commonly used calibrations tend to overestimate true values due to radiation from old stars and contributions from AGN
- Weak AGN-driven outflows revealed by optical spectra
- Study provides insights into properties and evolution of high stellar mass poststarburst galaxies
- Scientists studied five galaxies that had a lot of stars and were far away.
- They found that these galaxies had other smaller galaxies around them and faint features in their outer parts, which showed that interactions with other galaxies caused them to stop forming new stars.
- The original galaxies before they stopped forming stars had different amounts of stars, ranging from a few billion to a hundred billion.
- The burst of star formation happened a long time ago, but they could still see the effects of it for about 100 million years.
- Using special observations, scientists detected gas in four out of the five galaxies, and this gas was spread out over large distances.
Definitions
- Stellar masses: The amount of matter or stuff that makes up a star.
- Redshift: A way to measure how far away something is in space by looking at how its light is stretched or shifted towards redder colors.
- Quenching: When something stops or slows down a process, like when a galaxy stops forming new stars.
- Progenitors: The original or earlier versions of something.
- Observations: Looking carefully at something to learn more about it.
- Emission: Something being given off or released, like gas coming out from an object.
- Arcsecond: A small unit used to measure angles in space.
- Kiloparsecs: A very big distance measurement used in astronomy (1 kiloparsec = 1000 parsecs).
- Slit spectra
Exploring Poststarburst Galaxies with Multi-Wavelength Analysis
Poststarburst galaxies are a class of objects that have recently ceased their star formation activity. These galaxies are believed to be the transition phase between actively star-forming and quiescent galaxies, and thus provide important insights into the mechanisms of galaxy evolution. In a recent study, researchers conducted a comprehensive multi-wavelength analysis of five poststarburst galaxies at a redshift of approximately 0.7 and stellar masses greater than $10^{11} M_\odot$. The authors used optical images from the Subaru telescope and Hubble Space Telescope as well as optical spectra from the LEGA-C survey to explore these objects in detail. Additionally, ALMA observations were used to detect molecular gas emission in four out of the five studied galaxies. Here we summarize the findings from this research paper and discuss its implications for our understanding of poststarburst galaxies.
Galaxy Interactions: A Key Factor in Quenching Star Formation?
The authors observe a high incidence of companion galaxies and low surface brightness tidal features around these poststarburst systems, indicating that interactions between galaxies may play an important role in quenching star formation activity. This is further supported by their analysis of optical spectra which reveals weak AGN-driven outflows likely caused by interactions between two or more merging systems.
Star Formation Histories Revealed
By modeling the stellar continuum provided by LEGA-C survey data, the authors derive star formation histories for these poststarburst systems. They find that progenitors had stellar masses ranging from $2\times10^9 M_\odot$ to $10^{11} M_\odot$ and underwent an intense burst of star formation several hundred million years prior to observation before decaying on timescales estimated at approximately 100 million years.
Molecular Gas Detected but Low Star Formation Efficiency Observed
ALMA observations detect CO(2-1) emission in four out of five studied poststarburst systems with molecular gas masses reaching up to approximately $2 \times10^{10} M_\odot$. However, despite detecting molecular gas, 3 GHz continuum observations conducted by Very Large Array reveal no evidence for ongoing star formation within these objects due to their unresolved size scales (less than 1 arcsecond). Comparisons between observed star-formation rates (SFRs) and gas masses suggest low SFR efficiencies within these poststarburst systems; furthermore calibrations based on infrared or radio luminosities tend to overestimate true values due to radiation from old stars or contributions from active galactic nuclei (AGN).
Conclusions: Implications for Understanding Poststarbursts Galaxies
This study provides valuable insights into properties and evolution of massive ($M > 10^{11} M_\odot$) poststarbursts at redshifts near 0.7 through detailed multiwavelength analysis including optical imaging, spectroscopy, ALMA observations, 3GHz continuum measurements etc.. The results highlight importance galaxy interactions play in quenching process while emphasizing need accurate measurements SFRs order understand true nature such objects .
