"Red" but Not "Dead": Actively Star-forming Brightest Cluster Galaxies at Low Redshifts

"Red" but Not "Dead": Actively Star-forming Brightest Cluster Galaxies at Low Redshifts. Runge, J. & Yan, H. ArXiv e-prints, 1712:arXiv:1712.01482, December, 2017.

Paper abstract bibtex

Brightest Cluster Galaxies (BCGs) are believed to have assembled most of their stars early in time and, therefore, should be passively evolving at low redshifts and appear "red-and-dead." However, there have been reports that a minority of low-redshift BCGs still have ongoing star formation rates (SFR) of a few to even \${\textbackslash}sim\$100 \$M_{\textbackslash}odot/yr\$. Such BCGs are found in "cool-core" ("CC") clusters, and their star formation is thought to be fueled by "cooling flow." To further investigate the implications of low-redshift, star-forming BCGs, we perform a systematic search using the 22\${\textbackslash}mu\$m data ("W4" band) from the Wide-field Infrared Survey Explorer (WISE) on the GMBCG catalog, which contains 55,424 BCGs at \$0.1{\textbackslash}lesssim z{\textbackslash}lesssim 0.55\$ identified in the Sloan Digital Sky Survey (SDSS). Our sample consists of 389 BCGs that are bright in W4 ("W4BCGs"), most being brighter than 5 mJy. While some (\${\textbackslash}lesssim 20{\textbackslash}%\$) might host AGN, most W4BCGs should owe their strong mid-IR emissions to dust-enshrouded star formation. Their median total IR luminosity (\$L_\{IR\}\$) is \$5{\textbackslash}times10{\textasciicircum}\{11\} L_\{{\textbackslash}odot\}\$ (SFR \${\textbackslash}sim\$50 \$M_\{{\textbackslash}odot\}/yr)\$, and 27\textbackslash% of the whole sample has \$L_\{IR\}{\textgreater}10{\textasciicircum}\{12\} L_\{{\textbackslash}odot\}\$ (SFR \${\textgreater}\$100 \$M_\{{\textbackslash}odot\}/yr\$). Using ten W4BCGs that have Chandra X-ray data, we show that seven of them are possibly in CC clusters. However, in most cases (five out of seven) the mass deposition rate cannot account for the observed SFR. This casts doubt to the idea that cooling flows are the cause of the star formation in non-quiescent BCGs.

@article{runge_red_2017,
	title = {"{Red}" but {Not} "{Dead}": {Actively} {Star}-forming {Brightest} {Cluster} {Galaxies} at {Low} {Redshifts}},
	volume = {1712},
	shorttitle = {"{Red}" but {Not} "{Dead}"},
	url = {http://adsabs.harvard.edu/abs/2017arXiv171201482R},
	abstract = {Brightest Cluster Galaxies (BCGs) are believed to have assembled most of 
their stars early in time and, therefore, should be passively evolving
at low redshifts and appear "red-and-dead." However, there have been
reports that a minority of low-redshift BCGs still have ongoing star
formation rates (SFR) of a few to even \${\textbackslash}sim\$100 \$M\_{\textbackslash}odot/yr\$. Such BCGs
are found in "cool-core" ("CC") clusters, and their star formation is
thought to be fueled by "cooling flow." To further investigate the
implications of low-redshift, star-forming BCGs, we perform a systematic
search using the 22\${\textbackslash}mu\$m data ("W4" band) from the Wide-field Infrared
Survey Explorer (WISE) on the GMBCG catalog, which contains 55,424 BCGs
at \$0.1{\textbackslash}lesssim z{\textbackslash}lesssim 0.55\$ identified in the Sloan Digital Sky
Survey (SDSS). Our sample consists of 389 BCGs that are bright in W4
("W4BCGs"), most being brighter than 5 mJy. While some (\${\textbackslash}lesssim 20{\textbackslash}\%\$)
might host AGN, most W4BCGs should owe their strong mid-IR emissions to
dust-enshrouded star formation. Their median total IR luminosity
(\$L\_\{IR\}\$) is \$5{\textbackslash}times10{\textasciicircum}\{11\} L\_\{{\textbackslash}odot\}\$ (SFR \${\textbackslash}sim\$50 \$M\_\{{\textbackslash}odot\}/yr)\$,
and 27{\textbackslash}\% of the whole sample has \$L\_\{IR\}{\textgreater}10{\textasciicircum}\{12\} L\_\{{\textbackslash}odot\}\$ (SFR
\${\textgreater}\$100 \$M\_\{{\textbackslash}odot\}/yr\$). Using ten W4BCGs that have Chandra X-ray
data, we show that seven of them are possibly in CC clusters. However,
in most cases (five out of seven) the mass deposition rate cannot
account for the observed SFR. This casts doubt to the idea that cooling
flows are the cause of the star formation in non-quiescent BCGs.},
	urldate = {2018-01-03},
	journal = {ArXiv e-prints},
	author = {Runge, James and Yan, Haojing},
	month = dec,
	year = {2017},
	keywords = {Astrophysics - Astrophysics of Galaxies},
	pages = {arXiv:1712.01482},
}

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Such BCGs are found in \"cool-core\" (\"CC\") clusters, and their star formation is thought to be fueled by \"cooling flow.\" To further investigate the implications of low-redshift, star-forming BCGs, we perform a systematic search using the 22\\${\\textbackslash}mu\\$m data (\"W4\" band) from the Wide-field Infrared Survey Explorer (WISE) on the GMBCG catalog, which contains 55,424 BCGs at \\$0.1{\\textbackslash}lesssim z{\\textbackslash}lesssim 0.55\\$ identified in the Sloan Digital Sky Survey (SDSS). Our sample consists of 389 BCGs that are bright in W4 (\"W4BCGs\"), most being brighter than 5 mJy. While some (\\${\\textbackslash}lesssim 20{\\textbackslash}%\\$) might host AGN, most W4BCGs should owe their strong mid-IR emissions to dust-enshrouded star formation. 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Such BCGs\nare found in \"cool-core\" (\"CC\") clusters, and their star formation is\nthought to be fueled by \"cooling flow.\" To further investigate the\nimplications of low-redshift, star-forming BCGs, we perform a systematic\nsearch using the 22\\${\\textbackslash}mu\\$m data (\"W4\" band) from the Wide-field Infrared\nSurvey Explorer (WISE) on the GMBCG catalog, which contains 55,424 BCGs\nat \\$0.1{\\textbackslash}lesssim z{\\textbackslash}lesssim 0.55\\$ identified in the Sloan Digital Sky\nSurvey (SDSS). Our sample consists of 389 BCGs that are bright in W4\n(\"W4BCGs\"), most being brighter than 5 mJy. While some (\\${\\textbackslash}lesssim 20{\\textbackslash}\\%\\$)\nmight host AGN, most W4BCGs should owe their strong mid-IR emissions to\ndust-enshrouded star formation. Their median total IR luminosity\n(\\$L\\_\\{IR\\}\\$) is \\$5{\\textbackslash}times10{\\textasciicircum}\\{11\\} L\\_\\{{\\textbackslash}odot\\}\\$ (SFR \\${\\textbackslash}sim\\$50 \\$M\\_\\{{\\textbackslash}odot\\}/yr)\\$,\nand 27{\\textbackslash}\\% of the whole sample has \\$L\\_\\{IR\\}{\\textgreater}10{\\textasciicircum}\\{12\\} L\\_\\{{\\textbackslash}odot\\}\\$ (SFR\n\\${\\textgreater}\\$100 \\$M\\_\\{{\\textbackslash}odot\\}/yr\\$). Using ten W4BCGs that have Chandra X-ray\ndata, we show that seven of them are possibly in CC clusters. However,\nin most cases (five out of seven) the mass deposition rate cannot\naccount for the observed SFR. 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