Discovery of CIV Filaments in M87

Review of paper by Sparks, Pringle, Donahue, Carswell et. al. 2009, ApJ, 704, L20 (http://labs.adsabs.harvard.edu/adsabs/abs/2009ApJ...704L..20S/)

Journal Club talk, Astrophysics Research Institute (ARI), Liverpool John Moores University (LJMU), 4th December, 2009

Transcript

1. W.B. Sparks, J.E. Pringle, M. Donahue, R. Carswell et al. 2009, ApJ 704, L20 Discovery of CIV Filaments in M87 ARI Journal Club 4th December 2009
2. ❏ BACKGROUND: Optical Emission Line Filaments ❏ POSSIBLE FORMATION MECHANISMS ❏ PLAUSIBLE EXCITATION MECHANISMS ❏ THIS PAPER: OBSERVATIONS ANALYSIS DISCUSSION THERMAL CONDUCTION MODEL Outline
3. THE VIRGO CLUSTER & M87 to M87
7. Optical Emission Line Filamentary Structures ... have been seen in many “cool-core”clusters. NGC 1275 (Perseus A Seyfert galaxy): HST/ACS image ❏ At a distance of 230 million light-years, NGC 1275 is one of the closest giant elliptical galaxies and lies at the center of the Perseus cluster of galaxies. ❏ The red filaments are composed of cool gas being suspended by a magnetic field, and are surrounded by the 100-million-degree Fahrenheit hot gas. ❏ Gas is arrayed in a series of filaments extending over 30 kpc with an extension of 70 kpc to the north. ❏ Conselice et al. 2001, Sabra et al. 2000, Fabian et al. 2009
8. ... have been seen in many “cool-core”clusters. HST image of M87 with jet ❏ Similar filaments seen in the massive Virgo Cluster elliptical M87 ❏ Sabra et al. (2003) & Sparks et al. (2004) + others ❏ Filaments are wrapped around inner radio lobes. ❏ Filaments are dusty with the dust showing normal extinction characteristics. outflowing? interaction with jet? ❏ Filaments are also observed in NGC 4969 in Centaurus. Optical Emission Line Filamentary Structures
9. ❏ In many cool-core clusters the bright galaxy (BCG) has an excess of blue light indicative of recent star formation. Colors imply starbursts over 0.01 - 1 Gyr. ❏ About 1/3 of all BCGs have line-emission nebulae (Crawford etal. 1999) Many of these BCGs also contain reservoirs of 108 - 1011.5 Ms of molecular hydrogen. ❏ For these systems we can study the gas cooling from the ICM and accreting on to the galaxy. This is probably more common and important at high-redshift. ❏ Can be used to test theories for the growth of massive galaxies. Why do we care?
10. M87: X-RAY & RADIO ❏ From Chandra x-ray imaging: central regions are cooler than the outer parts of the cluster. Localised cool regions associated with the radio source. (Young, Wilson & Mundell 2002)
11. NGC 4911 NGC 4839 Plausible Formation Scenarios of Filaments The optical filaments (cool gas) are correlated with the x-ray filaments (hot gas) but the physical connection is not well understood. ❏ Condensations in a cooling intracluster medium (ICM) ❏ Cold interstellar material originating from galaxies and falling into the cluster core ❏ Already cold material originating in the central cluster galaxy i.e. central molecular gas buoyantly rising
12. NGC 4911 NGC 4839 Plausible Excitation Mechanisms For NGC 1275 and M87 PHOTOIONIZATION by ... ❏ CENTRAL AGN & ICM ❏ SHOCKS ❏ HOT YOUNG STARS “neither shocks not photoionization alone can reproduce the emission-line intensity ratios” (Sabra et al. 2003) ➛ some additional source of heating must be present. MOST LIKELY A COMBINATION OF PROCESSES
13. NGC 4911 NGC 4839 Plausible Excitation Mechanisms Optical line ratios in Abell 2597: Voit & Donahue (1997) ➛ SHOCKS ruled out as an excitation mechanism ➛ although HOT STARS are the best candidate for producing the ionization, even the hottest stars could power a nebula as hot as the one observed IFU Observations of emission nebulae around 6 BCGs: Hatch et al. (2007) ➛ Similar conclusions CHANDRA
14. NGC 4911 NGC 4839 Sources of EXTRA heating ❏ Relatively cool Hα + [ NII] emitting gas (~104 K) is immersed in a much hotter surrounding X-ray emitting medium. ➛ Thermal conduction? Sparks et al (1989) ❏ Range of gas temperatures in an interface region between the hot coronal ~ 107 K gas and the cooler ~ 104 K gas ❏ At intermediate temperatures, a major coolant is the strong CIV 1549 Å resonance line which arises from gas at 50,000 < T < 180,000 K [for M87 this line is redshifted to 1556 Å]
15. THIS PAPER Aim: to test a particular thermal conduction model of the filament and excitation by looking at CIV FUV emission
16. Observations: HST/ACS (SBC) ❏ observed four cool-core clusters ❏ used two FUV long-pass filters: F150LP and F165LP - difference effectively provides a CIV filter ❏ detection limits - 1/5 strength of the Hα + [NII] filaments observed in M87 ❏ filter choice solves “red leak” problem
17. Observations: HST/ACS (SBC) spatial resolution of ~0.034 x 0.030 “/pix nominal FOV of 34.6 x 30.1 arcseconds.
18. The FUV images synchrotron hotspot of radio jet?
19. The FUV images M87 subtracted using elliptical model from optical HST image - optical/FUV color gradient F606W = V band opical Hα + [NII] filaments GCs back. galaxies 2.5 kpc in projection
20. Analysis ❏ optical filaments (cool gas) and FUV filaments are spatially coincident ❏ data consistent with the filaments having a constant flux ratio ❏ filaments also observed in Chandra data (Sparks et al. 2004) ❏ flux calibrate optical and FUV filaments ❏ generate a mask to isolate the FUV emission: 8 x 10-5 counts s-1. point sources and hot spot are also removed
21. Analysis CIV Hα + [NII] ❏ total power of CIV: 1.1 x 10 39 erg s-1 ❏ two most obvious candidates: hot gas (~ 10 5 K) and stars.
22. Discussion ❏ FUV flux limit corresponds to L (B0V star) based on Kurucz models. ❏ Stars earlier than B0V with a min mass, M = 17.5 MS should be seem as individual point sources. ❏ For a population of hot stars: Total burst mass: M (stars) = 2.14 x 103 Ms # (stars) M > Mmin = 14. -- not a plausible of description of filament morphology.
23. Theoretical Conduction Model ❏ while the assumptions for the fiducial model are unlikely to be correct on all scales at all times, they may be a good approximation on small scales where most of the optical and UV emitting gas resides, and for the most prominent filaments. ❏ model predicts: CIV flux ~ 5 x 1039 erg s-1 for a pressure of 8 x 10-10 dynes cm-2 ❏ observed: CIV flux ~ 1.1 x 1039 erg s-1 ❏ significant sensitivity to geometry, inner radius, pressure
24. THANK YOU