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Cool Molecular Gas (and SF) in Central Cluster Giant Elliptical Galaxies

Jeremy Lim, Hong Kong University. Cool Molecular Gas (and SF) in Central Cluster Giant Elliptical Galaxies . Central cluster cD galaxies can be very rich in molecular gas, with M(H 2 ) ≈ 10 9-11 M 

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Cool Molecular Gas (and SF) in Central Cluster Giant Elliptical Galaxies

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  1. Jeremy Lim, Hong Kong University Cool Molecular Gas (and SF) in Central Cluster Giant Elliptical Galaxies • Central cluster cD galaxies can be very rich in molecular gas, with M(H2) ≈ 109-11 M • CO line profiles usually not double horned, unlike that in many other elliptical galaxies which where well mapped exhibit rotating disks • In NGC 1275 (only central cluster cD galaxy well mapped in CO), molecular gas distributed in radial filaments with kinematics indicating free fall • Central cD galaxies can show recent star formation, albeit at relatively low levels and in NGC 1275 not obviously related to bulk of molecular gas

  2. Surveys motivated by prediction that X-ray cooling flows should deposit copious amounts of cool gas at center of clusters (Cowie & Binney 1977; Fabian & Nulsen 1977) Mass of cool molecular gas X-ray cooling-flow cluster (Perseus cluster) Non X-ray cooling-flow cluster (Coma cluster)

  3. Surveys motivated by prediction that X-ray cooling flows should deposit copious amounts of cool gas at center of clusters (Cowie & Binney 1977; Fabian & Nulsen 1977) • Recent surveys target central cD galaxies of clusters suspected to harbor strong X-ray cooling flows, pushing out to z~0.4 (Edge 2001; Salomé & Combes 2003) • 21-28 of 56 galaxies (40%-50%) detected in CO with M(H2)≈109-11 M Mass of cool molecular gas NGC 1275 M(H2) (M) 1011 1010 Detections 109 Non-Detections Redshift (z)

  4. Surveys motivated by prediction that X-ray cooling flows should deposit copious amounts of cool gas at center of clusters (Cowie & Binney 1977; Fabian & Nulsen 1977) • Recent surveys target central cD galaxies of clusters suspected to harbor strong X-ray cooling flows, pushing out to z~0.4 (Edge 2001; Salomé & Combes 2003) • 21-28 of 56 galaxies (40%-50%) detected in CO with M(H2)≈109-11 M • Surveys of nearby (z ≤ 0.02) elliptical galaxies not at cluster centers find M(H2) ≤ 109 M (Lees et al. 1991; Wiklind et al. 1995; Knapp & Rupen 1996; Combes et al. 2007; Sage et al. 2007) Mass of cool molecular gas

  5. Survey of all 3C elliptical galaxies at z ≤ 0.031 reveal that all but NGC 1275 (host of 3C 84, central cD galaxy of Perseus Cluster) have M(H2) ≤ 109 M (Lim et al. 2004) Mass of cool molecular gas Mass of Molecular Gas in 3C Elliptical Radio Galaxies at z ≤ 0.031 Number of Galaxies 3C 84 (NGC 1275) 3C 31 107 108 109 1010 Mass of Molecular Hydrogen Gas (M) Lim et al. (2004)

  6. CO line profiles of central cluster cD galaxies usually not double horned (indicative of rotating disks) • All other elliptical galaxies (including those in clusters but not at centers) well mapped in CO exhibit rotating disks Distribution of cool molecular gas NGC 1275 (z=0.018) M(H2) ≈ 2 x 1010 M RXJ0821+07 (z=0.110) M(H2) ≈ 4 x 1010 M Mirabel et al. (1989) Abell 1835 (z=0.252) M(H2) ≈ 2 x 1011 M Abell 1068 (z=0.139) M(H2) ≈ 9 x 1010 M Edge (2001)

  7. NGC 1275 (host of 3C 84), at center of the Perseus Cluster (which is suspected to harbor a strong X-ray cooling flow), so far only central cluster cD galaxy well mapped in CO Distribution of cool molecular gas Near-IR image of NGC 1275 10 kpc

  8. Molecular gas near center concentrated in multiple radial filaments (Lim, Ao, & Dinh 2008; Salomé et al. 2008; Ho, Lim, & Dinh 2009) Distribution of cool molecular gas CO(2-1) image of NGC 1275 10 kpc Lim et al. (2008)

  9. Molecular gas near center concentrated in multiple radial filaments (Lim, Ao, & Dinh 2008; Salomé et al. 2008; Ho, Lim, & Dinh 2009) • Filaments have lengths of 1-3 kpc Distribution of cool molecular gas CO(2-1) image of NGC 1275 10 kpc (2.8 kpc) (1.4 kpc) (~1 kpc) (~1 kpc) (2.3 kpc) (2.6 kpc) Lim et al. (2008)

  10. Molecular gas near center concentrated in multiple radial filaments (Lim, Ao, & Dinh 2008; Salomé et al. 2008; Ho, Lim, & Dinh 2009) • Filaments have masses of ~108 M to ~109 M Distribution of cool molecular gas CO(2-1) image of NGC 1275 10 kpc (1 x 109 M) (3 x 108 M) (3 x 108 M) (1 x 108 M) (5 x 108 M) (2 x 109 M) Lim et al. (2008)

  11. Molecular gas near center concentrated in multiple radial filaments (Lim, Ao, & Dinh 2008; Salomé et al. 2008; Ho, Lim, & Dinh 2009) • No globally-ordered motion such as rotation, arguing against minor merger with gas-rich galaxy Distribution of cool molecular gas CO(2-1) image of NGC 1275 10 kpc Lim et al. (2008)

  12. Longest filaments E and W of center have linearly increasing blueshifted velocity with decreasing radius CO(2-1) image of NGC 1275 Distribution of cool molecular gas PV-diagrams in CO(2-1) Lim et al. (2008)

  13. Kinematics consistent with free-fall in grav potential of NGC 1275 Free-fall trajectories Distribution of cool molecular gas PV-diagrams in CO(2-1) Lim et al. (2008)

  14. Suggests molecular gas condensed from hot intracluster medium • Mass deposition rate into filaments several 10s M/yr X-ray color image of NGC 1275 Distribution of cool molecular gas radio jet CO(2-1) Lim et al. (2008)

  15. Many (>50%) central cD galaxies of clusters suspected to harbor X-ray cooling flows show increasingly bluer color towards center suggestive of massive star formation (Rafferty et al. 2008) Star formation CF clusters mostly non-CF clusters U - R Rafferty et al. (2008) Equivalent radius (arcsec)

  16. Recent star formation in NGC 1275: i) ~2000 compact (≤1.5 pc) and massive (107-8 M) blue star clusters with ages 100s Myr concentrated around center (R ≤ 4 kpc) (Holtzman et al. 1992; Carlson et al. 1998) Star formation Optical continuum (bluish white) of NGC 1275 1 kpc Carlson et al. (1998)

  17. Recent star formation in NGC 1275: ii) young star clusters closely associated with many outer filaments Star formation Hα (red) + optical continuum (bluish white) of NGC 1275 10 kpc Fabian et al. (2008)

  18. Recent star formation in NGC 1275: ii) young star clusters closely associated with many outer filaments Star formation Hα (red) + optical continuum (bluish white) of NGC 1275 10 kpc Fabian et al. (2008)

  19. At least ~half of central cD galaxies in clusters suspected to harbor strong X-ray cooling flows are very rich in molecular gas, with M(H2) ≈ 109-11 M • CO line profiles usually not double horned, unlike that in many other elliptical galaxies which where well mapped exhibit rotating disks • In NGC 1275 (only central cluster cD galaxy well mapped in CO), molecular gas in free-fall suggesting accretion from hot intracluster medium rather than galactic cannibalisms • Many central cD galaxies of clusters suspected to harbor strong X-ray cooling flows show low levels of recent star formation, which in NGC 1275 not related to bulk of molecular gas Summary

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