The ACS Coma Cluster Treasury Survey: Velocity dispersions of cluster galaxies from Keck/DEIMOS spectra

Invited Seminar talk at the Department of Astronomy, University of Nottingham, 26th May 2010,

Based on two published papers:
Dwarf galaxies in the Coma cluster - I. Velocity dispersion measurements
Kourkchi et al. 2012, MNRAS, 420, 2819-2834
http://labs.adsabs.harvard.edu/adsabs/abs/2012MNRAS.420.2819K/

Dwarf galaxies in the Coma cluster - II. Spectroscopic and photometric fundamental planes
Kourkchi et al. 2012, MNRAS, 420, 2835-2850
http://labs.adsabs.harvard.edu/adsabs/abs/2012MNRAS.420.2835K/

Transcript

1. Nottingham Seminar, 26th May 2010 Arna Karick (LJMU) Ehsan Kourkchi (Sharif) Habib Khosroshahi (Sharif) Dave Carter (LJMU) Velocity dispersions of cluster galaxies from Keck/DEIMOS spectra The ACS Coma Cluster Treasury Survey
2. ❏ Why is Coma Special? ❏ The HST/ACS Coma Cluster Treasury Survey ❏ Science Highlights ❏ Keck/DEIMOS Spectroscopy of cluster galaxies ❏ Structural Parameter Analysis ❏ Other Projects ❏ Conclusions Talk Outline
3. WHY STUDY THE COMA CLUSTER?
4. ❏ Nearest rich and densely populated cluster in the local (z ~0.023 ~100 Mpc) universe. ρgal ∼ 104 Mpc-3 in the core. Several times more dense than Virgo. ❏ Bright extragalactic x-ray source. ❏ Complex cluster environment. x-ray substructure & infalling galaxies. ❏ Large samples of cluster galaxies have been studied. ❏ Local benchmark for comparative studies of galaxy evolution in different environments. Why is Coma Special?
5. NGC 4911 NGC 4839 Neumann et al. (2003) NGC 4889 ❏ Substructure revealed by ROSAT X-ray surface brightness profile out to 100′. (Briel et al. 1992, White et al. 1993) ❏ Strong evidence for NGC 4839 falling in for the first time. (Neumann et al. 2001) ❏ NGC 4839 has already passed through the centre. (Burns et al. 1994) ❏ E+A galaxies correlate with X-rays (?) ❏ Cluster substructure from velocities of ~550 cluster galaxies. (Colless & Dunn 1993) ⟨vel⟩ = 6853 km s-1, σ = 1083 km s-1 ❏ Significant difference in velocity between NGC 4889 and NGC 4874 indicative of a recent merger. (Fitchett & Webster 1987) Why is Coma Special? NGC 4874
6. The Universe As We Know It Low-redshift benchmark for galaxy cluster formation. Fiducial reference for fundamental plane studies of early-type galaxy evolution.
7. The Universe As We Know It Next generation telescopes: JWST, TMT, ELT will focus on the “birth” of galaxies at z ~ 6 − 8
8. Next generation telescopes: JWST, TMT, ELT will focus on the “birth” of galaxies at z ~ 6 − 8 The Universe As We Know It
9. Compare observations with predictions of hierarchical and evolutionary models of galaxy formation
10. http://astronomy.swin.edu.au/coma/index-mm.htm http://www.astro.ljmu.ac.uk/research/coma.shtml The HST/ACS Coma Cluster Treasury Survey
11. ❏ Cycle 15 ACS Treasury Survey (PI: Carter) ❏ Covers ~270 arcmin2 of the cluster core and infall region ❏ F814W (I) and F475W (g) band images ❏ FOV: 202″ x 202″ (11.3 arcmin2), resolution of 0.05″ ❏ Observing program terminated due to ACS failure + 7 FIELDS The Survey Professor David Carter (PI) - UK Prof. Steve Phillipps - UK Dr Avon P. Huxor - UK Mr James Price - UK Dr Mustapha Mouhcine - UK Dr Carlos Hoyos - UK Dr Neil Trentham - UK Dr John Lucey - UK Prof. Ray M. Sharples - UK A Prof. Alister Graham - Australia Mr Juan Madrid - Australia Dr Harry C. Ferguson (PI) - US Dr Jennifer Lotz - US Dr Neal A. Miller - US Dr. Brent Tully - US Dr. Kristin Chiboucas - US Prof. Bahram Mobasher - US Dr Paul Goudfrooij - US Mr Derek Hammer - US Dr Ann Hornschemeier - US Dr Dan Batcheldor - US Prof. David Merritt - US Dr Ron Marzke - US Dr Rafael Guzman - US Dr Thomas H. Puzia - Canada Dr Terry Bridges - Canada Dr Habib Khosroshahi - ARI/Iran Mr. Ehsan Kourkchi - ARI/Iran Dr Carlos del Burgo- Ireland Dr Bryan Miller - Chile Dr Bianca Poggianti - Italy Dr Alfonso Aguerri - Spain Dr Marc Balcells - Spain Dr Reynier Peletier - Netherlands Mr Mark den Brok - Netherlands Prof. Edwin Valentijn - Netherlands Dr Gijs Verdoes Kleijn - Netherlands Dr Peter Erwin - Germany Dr Yutaka Komiyama - Japan Dr Masafumi Yagi - Japan Dr Eric Peng - China
12. The Survey Figure 1. from Hammer et al. (2010) The HST/ACS Coma Cluster Survey II: Data Description and Source Catalogs Professor David Carter (PI) - UK Prof. Steve Phillipps - UK Dr Avon P. Huxor - UK Mr James Price - UK Dr Mustapha Mouhcine - UK Dr Carlos Hoyos - UK Dr Neil Trentham - UK Dr John Lucey - UK Prof. Ray M. Sharples - UK A Prof. Alister Graham - Australia Mr Juan Madrid - Australia Dr Harry C. Ferguson (PI) - US Dr Jennifer Lotz - US Dr Neal A. Miller - US Dr. Brent Tully - US Dr. Kristin Chiboucas - US Prof. Bahram Mobasher - US Dr Paul Goudfrooij - US Mr Derek Hammer - US Dr Ann Hornschemeier - US Dr Dan Batcheldor - US Prof. David Merritt - US Dr Ron Marzke - US Dr Rafael Guzman - US Dr Thomas H. Puzia - Canada Dr Terry Bridges - Canada Dr Habib Khosroshahi - ARI/Iran Mr. Ehsan Kourkchi - ARI/Iran Dr Carlos del Burgo- Ireland Dr Bryan Miller - Chile Dr Bianca Poggianti - Italy Dr Alfonso Aguerri - Spain Dr Marc Balcells - Spain Dr Reynier Peletier - Netherlands Mr Mark den Brok - Netherlands Prof. Edwin Valentijn - Netherlands Dr Gijs Verdoes Kleijn - Netherlands Dr Peter Erwin - Germany Dr Yutaka Komiyama - Japan Dr Masafumi Yagi - Japan Dr Eric Peng - China
13. Science Highlights ❏ The HST/ACS Coma Cluster Survey I - Survey objectives and design (Carter et al. 2008) ❏ *The HST/ACS Coma Cluster Survey II - Data description and source catalogs (Hammer et al. 2010 - submitted) ❏ *The HST/ACS Coma Cluster Survey III - Catalog of Structural Parameters of galaxies using (Hoyos et al. 2010 - submitted) single Sersic fits ❏ The HST/ACS Coma Cluster Survey V - Compact Stellar Systems in the Coma Cluster (Price et al. 2009) ❏ The HST/ACS Coma Cluster Survey VI - The Galaxy Luminsosity Function (Trentham et al. 2010 - submitted) ❏ Keck/LRIS Spectroscopic confirmation of Coma Cluster dwarf galaxy membership assignments (Chiboucas et al. 2010 - submitted) ❏ **Kinematic Properties of faint early type galaxies in the Coma Cluster (Kourkchi et al. 2010 - in prep) ❏ Stellar Populations of faint early type galaxies in the Coma Cluster (Karick et al. 2010 - in prep) ❏ **Thirteen gaseous stripping events in the Coma Cluster (Smith et al. 2010 - submitted)
14. Science Highlights ❏ Keck/LRIS Spectroscopic confirmation of Coma Cluster dwarf galaxy membership assignments (Chiboucas et al. 2010 - submitted)
15. Science Highlights ❏ **Thirteen gaseous stripping events in the Coma Cluster (Smith et al. 2010 - submitted)
16. Science Highlights ❏ The HST/ACS Coma Cluster Survey VI - The Galaxy Luminsosity Function (Trentham et al. 2010 - submitted)
17. Keck/DEIMOS Spectroscopy http://keckobservatory.org/
18. ❏ What fraction of cluster galaxies are dwarfs? Motivation Figure 4. Trentham et al. (2010) - submitted
19. ❏ What fraction of cluster galaxies are dwarfs? ❏ What is their dark matter content? Motivation
20. ❏ What fraction of cluster galaxies are dwarfs? ❏ What is their dark matter content? ❏ Do they follow the same “Fundamental Scaling relations” as giant galaxies? Motivation (1) “scaling laws” reveal a great deal about the physical process governing galaxy formation (2) Faber−Jackson (1976) relation for ellipticals: L ∝ σα (α≈4) (3) α helps constrain galaxy formation models. (Dekel & Silk 1986) ➙ α=5.26 galaxies dominated by dark matter ➙ α=2.70 galaxies with little dark matter + const. M/L (4) Globular cluster relation: L ∝ σα (α=1.7) Evstigneeva et al. (2006) Luminosity vs. Velocity dispersion
21. ❏ What fraction of cluster galaxies are dwarfs? ❏ What is their dark matter content? ❏ Do they follow the same “Fundamental Scaling relations” as giant galaxies? ❏ Can we quantify the environmental impact on dwarf galaxy evolution? Motivation (1) “scaling laws” reveal a great deal about the physical process governing galaxy formation (2) Faber−Jackson (1976) relation for ellipticals: L ∝ σα (α≈4) (3) α helps constrain galaxy formation models. (Dekel & Silk 1986) ➙ α=5.26 galaxies dominated by dark matter ➙ α=2.70 galaxies with little dark matter + const. M/L (4) Globular cluster relation: L ∝ σα (α=1.7)
22. Keck/DEIMOS Spectroscopy of Cluster Galaxies OBSERVATIONS: March 2007 ❏ Two DEIMOS masks (~6600s) ~200 galaxies ❏ Instrument spectral resolution (red): 1.6 Å (FWHM), pixel size : 0.30 Å ❏ Blue grating (900ZD l/mm, 5500 blaze) wavelength range: 4100 – 7500 Å : Line-strength indices ❏ Red grating (1200G l/mm, 7500 blaze) wavelength range: 7500‐ 11000 Å : Velocity dispersions
23. ❏ Two DEIMOS masks (~6600s) ~200 galaxies ❏ Instrument spectral resolution (red): 1.6 Å (FWHM), pixel size : 0.30 Å ❏ Blue grating (900ZD l/mm, 5500 blaze) wavelength range: 4100 – 7500 Å : Line-strength indices ❏ Red grating (1200G l/mm, 7500 blaze) wavelength range: 7500‐ 11000 Å : Velocity dispersions Keck/DEIMOS Spectroscopy of Cluster Galaxies OBSERVATIONS: March 2007 OBSERVATIONS: March 2007
24. Keck/DEIMOS Spectroscopy of Cluster Galaxies Source Selection: ❏ within ±3σ of the red sequence in a (B-R) vs. R color-magnitude diagram : -19 < MR < -16 mag ❏ galaxy morphology checked in ACS imaging ❏ 1.0” width slits for radial velocity measurements of LSB galaxies (cluster candidates) ❏ 0.7” width slits for velocity dispersion analysis
25. Keck/DEIMOS Spectroscopy of Cluster Galaxies Redshift Analysis: ❏ 50/50 galaxies are confirmed cluster members ❏ 70/153 LSB galaxy candidates are background galaxies. (rest are too low S/N) ❏ 33 UCD (bright IGC) candidates: 9/33 stars/background galaxies 8/33 probable Coma members
26. Velocity dispersions of cluster galaxies ❏ 0.7” width slits. Dispersion: 0.33 Å/pix. Resolving power, R = 5000 (velocity width ~ 25 km s-1) ❏ Spectra reduced using the DEEP2 IDL pipeline ❏ 41 galaxies with S/N ≥ 15 luminosities: − 20.5 ≤ M r (SDSS) ≤ − 15.0 mag ❏ For these galaxies we can measure dispersions down to 15 km s-1 Velocity dispersions measured from CaT absorption lines (CaII: 8498Å, 8542Å and 8662Å - weak dependence on metallicity) Analysis of red setup: 7500A - 9000A, CaT analysis (Kourkchi et al. 2010, in prep)
27. Measurements from the CaT region: not trivial! SKY LINES are redshifted to CaT Velocity Dispersions − the data
28. pPXF: Cappellari & Emsellem (2004) - templates selected from the Indo-US stellar library (+ three DEIMOS templates) - radial velocity and dispersion determined simultaneously by minimising the X2 - uses multiple weighted stellar templates (~50-80) and finds best fit solution - no need to do simulation before any measurement - less sensitive to S/N ratio than other methods - results agree well with Cody et al. (2008) for S/N >15 FXCOR: Tonry & Davis (1979) - simulation needed before any measurement - to check cross-correlation - very sensitive to low S/N ratio spectra - need to use many stellar templates in order to get reliable results Velocity Dispersions − analysis
29. pPXF: Cappellari & Emsellem (2004) - THE DETAILS - pPFX works in pixel space and uses Guass-Hermite series to extract the radial velocity and dispersion simultaneously by minimising the X2 - galaxy spectrum and template spectra are rebinned linearly in wavelength x = ln (λ) - model spectrum obtained by convolving the template and a broadening function. - for low S/N pPXF supresses the noise effects in the solution Errors and Uncertainties (i) “statistical error” - simulated galaxy spectra with variable S/N, errors due to random noise (ii) template mismatch - measurement limited to CaT region Velocity Dispersions − analysis
30. Luminosity: SDSS Mr log (velocity dispersion) Matkovic et al. (2005) KPNO/WIYN Hydra fibre spectroscopy Mgb and Hβ lines used to measure dispersions (stronger metallicity dependence) RESULTS: Faber-Jackson Relation ( L ∝σα )
31. Luminosity: SDSS Mr log (velocity dispersion) Cody et al. (2008) KPNO/WIYN Hydra fibre spectroscopy of early type galaxies −20.6 < MR < -15.7 Mgb and Hβ lines used to measure dispersions 60% galaxies have S/N <10 α = 2.0 ± 0.2 inner < 0.5 deg α = 2.21 ± 0.4 Outer > 0.5 deg α = 1.29 ± 0.29 RESULTS: Faber-Jackson Relation ( L ∝σα )
32. RESULTS: Faber-Jackson Relation ( L ∝σα ) Luminosity: SDSS Mr log (velocity dispersion) S/N < 15 Kourkchi et al. (2010) - in prep PhD Thesis
33. RESULTS: Faber-Jackson Relation ( L ∝σα ) Luminosity: SDSS Mr log (velocity dispersion) α = 2.73 ± 0.06 for DEIMOS galaxies with S/N > 15 α = 2.62 ± 0.03 for K10 + M05 samples α = 2.45 ± 0.02 for K10 + M05 +C08 samples
34. RESULTS: Faber-Jackson Relation ( L ∝σα ) Science Questions: ❏ does the relation flatten? ❏ Is the scatter at the faint end dependent on other parameters? i.e. Sersic index? or μeff? (Graham & Guzman 2003) ❏ Are deviations from Sérsic profiles due to distinct types of early type galaxy? (Kormendy et al. 2009) − “missing light” at small radii ➛ scouring by binary black holes − “extra light” at small radii ➛ starbursts following dissipative mergers − rotation? (Emsellem et al. 2007)
35. STRUCTURAL PARAMETER ANALYSIS http://keckobservatory.org/
36. THE STRUCTURAL PARAMETERS CATALOGUE ❏ ~ 10,000 galaxies in 25 Coma fields. ❏ All galaxies with <μ> brighter than 24.5 mag arcsec2 ❏ SExtractor source detection, photometry and basic geometric parameters (inc. S/G class) ❏ GIM2D Single Sérsic fits (n), bulge-disk parameters ❏ GALFIT Single Sérsic fits (n), effective radii (re), surface brightesses (μ), bulge-disk parameters ❏ Error and completeness (magnitude and size) analysis from GEMS simulations. ❏ Available to the astronomical community at ASTRO-WISE and MAST. ❏ Complements two other HST surveys: Based on F814W ACS images: Hoyos et al (2010), Mark den Brok - PhD STAGES: Abell 901/2 at redshift z~ 0.165 (Grey et al. 2009) GEMS: 900 arcmin2 region within the Extended Chandra DFS (Rix et al. 2004)
37. RESULTS: Structural Analysis Kourkchi et al. (2010) in prep
38. RESULTS: Structural Analysis Kourkchi et al. (2010) in prep ❏ typical Reff are less than 1.6 kpc
39. RESULTS: Structural Analysis Kourkchi et al. (2010) in prep
40. Work in Progress ❏ Non-standard setup - wavelength calibration tricky! (optical model results in ~45Å error) ❏ DEIMOS optimized for red setup. Low throughput restricts us to ~5000 - 6500Å (ie. Hβ, Mg, Fe) (at least for most galaxies) ❏ AIM: combine with velocity dispersion results and compare with previous work (eg. Matkovic & Guzman 2005) Analysis of blue setup: 3900A - 6700A, Line-strength indices (Karick et al. 2010, in prep)
41. Conclusion ❏ The ACS Coma Cluster Treasury Survey. ❏ Science Highlights: UCDs, LSB galaxies and galaxy stripping. ❏ Keck/DEIMOS observations of ~200 confirmed and “likely” cluster members ❏ Accurate velocity dispersions for ~40 cluster galaxies down to 20 kms-1 α = 2.73 ± 0.06 for 38 dwarf galaxies with S/N >15 ❏ Fundamental Plane: investigating the dependence on structural parameters. ❏ Structural Parameters Catalogue: Available mid-2010 on ASTRO-WISE and MAST ❏ Future Work: Detailed structural parameter study of SPC sub-samples
42. ...THANKS ❏ Keck/DEIMOS spectroscopy of Coma Cluster UCDs/IGCs (with Michael Gregg & Michael West) ❏ UV/Optical properties of Fornax Cluster galaxies (with Michael Gregg & Soo-Chang Rey) ❏ Magellan/IMACS spectroscopy of ~60 Fornax Cluster UCDs/GCs (with Michael Gregg & Marla Geha) ❏ CTIO/ugriz imaing of Fornax Cluster galaxies and UCDs (with Michael Gregg & Michael Drinkwater) ❏ Keck/HIRES+LGSAO observations of bright M31 Globular Clusters (with Michael Gregg) ❏ 6dF spectroscopy of Fornax Cluster galaxies - E+As? (with Michael Drinkwater)