1

Lei Bai Lei Bai

George George RiekeRieke

Marcia RiekeMarcia Rieke

Steward Steward ObservatoryObservatory

Infrared Luminosity Function of Infrared Luminosity Function of the Coma Clusterthe Coma Cluster

2

BackgroundBackgroundInfrared emission from galaxies:Infrared emission from galaxies:

late-type galaxies ==> stronglate-type galaxies ==> strong

early-type galaxies ==> weakearly-type galaxies ==> weak

Galaxy clusters, dominated by early-type galaxies, Galaxy clusters, dominated by early-type galaxies, are unlikely to be strong sources in the far-infraredare unlikely to be strong sources in the far-infrared

The large velocity dispersion in clusters also suggests The large velocity dispersion in clusters also suggests that very luminous infrared galaxies would be rare.that very luminous infrared galaxies would be rare.

Stripping may remove the ISM so star formation Stripping may remove the ISM so star formation would be reduced (but maybe star formation could be would be reduced (but maybe star formation could be induced by compression provided by the intracluster induced by compression provided by the intracluster medium)medium)

So is the population of galaxies in a cluster So is the population of galaxies in a cluster fundamentally different in their infrared properties?fundamentally different in their infrared properties?

Some clusters also contain intracluster gas. Is there Some clusters also contain intracluster gas. Is there any dust associated with this gas? Enough to be any dust associated with this gas? Enough to be detectable in the infrared?detectable in the infrared?

3

IRAS Detected IRAS Detected Spirals in the Spirals in the

Hercules ClusterHercules Cluster

Young et al. 1984 ApJL 278 75Young et al. 1984 ApJL 278 75

4

ISO Observations of ComaISO Observations of ComaISO Observations of ComaISO Observations of Coma

Stickel et al. scanned ISOPHOT Stickel et al. scanned ISOPHOT across the face of Coma at across the face of Coma at 120120m and at 185m and at 185m. They did m. They did not claim to detect individual not claim to detect individual galaxies but interpret their galaxies but interpret their results as showing an extended results as showing an extended cool dust component:cool dust component:

- ~0.1 MJy/sr = 4x10- ~0.1 MJy/sr = 4x104343 ergs/sergs/s

Assuming a dust temperature Assuming a dust temperature in the range of 25-40K, this in the range of 25-40K, this corresponds to corresponds to 6.2x106.2x1077MM < < MMDustDust < 1.6x10 < 1.6x1099M M for r<0.2Mpc. for r<0.2Mpc.

Comparison with x-ray impliesComparison with x-ray implies

MMdust/ dust/ MMgasgas between 1.3x10 between 1.3x10-5 -5 and and 3.2x103.2x10-4-4

5

Spitzer Observes ComaSpitzer Observes Coma

Coma was Coma was observed in observed in scan map scan map mode with an mode with an equivalent of equivalent of 88 seconds 88 seconds exposure time exposure time at 24at 24m and m and 40 seconds at 40 seconds at 7070m. m.

Photometry of Photometry of objects was objects was obtained using obtained using Sextractor.Sextractor.

2 degs

• • 2424m detectionm detectionLLIRIR>10>1043.343.3 erg/s erg/s

NGC 4836 region

6

7 arc min7 arc min Clusters members are Clusters members are circled.circled.

Coma Core at 24Coma Core at 24mm

R (0.7R (0.7m)m) 24 24 mm

7

Detection StatisticsDetection Statistics

Cluster membership was determined by matching Cluster membership was determined by matching 2424m and 70m and 70m sources with galaxies from the m sources with galaxies from the spectroscopic surveys of Beijersbergen and van de spectroscopic surveys of Beijersbergen and van de Hulst (2003) and Mobasher et al. 2001.Hulst (2003) and Mobasher et al. 2001.

MIPS 24MIPS 24m detected 217 of 498 galaxies in BvdHm detected 217 of 498 galaxies in BvdH

7070m detected 58 of 477 galaxies in BvdHm detected 58 of 477 galaxies in BvdH MIPS 24MIPS 24m detected 123 of 333 galaxies in M et al.m detected 123 of 333 galaxies in M et al.

7070m detected 33 of 303 galaxies in M et al.m detected 33 of 303 galaxies in M et al. Because a much larger fraction of cluster members Because a much larger fraction of cluster members

are detected at 24are detected at 24m, we derived infrared m, we derived infrared luminosities from this wavelengthluminosities from this wavelength

SEDs and R/24SEDs and R/24m ratios were used to calculate the m ratios were used to calculate the luminosities.luminosities.

8

Spectral Energy DistributionsSpectral Energy Distributions

Offset vertically for clarity. SEDs from Offset vertically for clarity. SEDs from Devriendt et al. 1999Devriendt et al. 1999

This sample of This sample of SEDs is SEDs is weighted weighted towards towards luminous IR luminous IR galaxies. There galaxies. There are no galaxies are no galaxies earlier than S0 earlier than S0 so a check is so a check is needed needed whether there whether there are biases for are biases for early-type early-type galaxies.galaxies.Soon we can use a Soon we can use a Spitzer collection of Spitzer collection of SEDs!SEDs!

9

• SED templates 70m completeness

early-type

late-type

solid = 70m detection

Deriving IR LuminositiesDeriving IR Luminosities

If the suite of SEDs If the suite of SEDs represents all types of represents all types of galaxies, then a galaxies, then a correlation between correlation between colors and 8-1000colors and 8-1000m m luminosity can be luminosity can be derived. derived.

We use the colors We use the colors SS2424/S/Sr(0.7) r(0.7)

and Sand S7070//SS2424

derive a relation derive a relation between Sbetween S2424 and IR and IR luminosity.luminosity.

Note that early-type Note that early-type galaxies have the same galaxies have the same behavior as late-type behavior as late-type galaxies which are galaxies which are much more common in much more common in the SED template set.the SED template set.

10

• Coma galaxies

Spirals

Luminous IR galaxy

Ultra luminous IR galaxy

Lagache et al. 2003 normal spiral

Fitting Colors to Get Fitting Colors to Get LuminosityLuminosity

Notice small range in LNotice small range in LIRIR/L/L2424: Fitting colors almost : Fitting colors almost unnecessary, no bias introduced by optical unnecessary, no bias introduced by optical selection.selection.

Open symbols show values derived from templates; Open symbols show values derived from templates; dots show application of fit to Coma galaxies.dots show application of fit to Coma galaxies.

11

24m completeness limit

MBC completeness limit

BvdHC completeness limit

MBC = Mosbasher MBC = Mosbasher et al. deeper but et al. deeper but only on coreonly on core

BvdHC = BvdHC = Beijersbergen and Beijersbergen and van de Hulstvan de Hulst covers covers larger area less larger area less deeplydeeply

Cluster Luminosity FunctionCluster Luminosity Function

Luminosity function shown is for projected area of cluster.Luminosity function shown is for projected area of cluster.

Schecter Function fits:Schecter Function fits:

MBC MBC = 1.52±0.13 = 1.52±0.13

log(Llog(L**(IR)/L(IR)/L) = 10.72 ± ) = 10.72 ± 0.700.70

BvdHC BvdHC = 1.42±0.09 = 1.42±0.09

log(Llog(L**(IR)/L(IR)/L) = 10.52 ± ) = 10.52 ± 0.250.25

12

Comparison to Field LFComparison to Field LFComa:Coma: Field* (z=0-0.2): Field* (z=0-0.2):

MBC MBC = 1.52±0.13 = 1.52±0.13 = 1.23±0.0.07 = 1.23±0.0.07

log(Llog(L**(IR)/L(IR)/L) = 10.72 ± 0.70 log(L) = 10.72 ± 0.70 log(L**(IR)/L(IR)/L) = 10.36 ± 0.14) = 10.36 ± 0.14

BvdHC BvdHC = 1.42±0.09 = 1.42±0.09

log(Llog(L**(IR)/L(IR)/L) = 10.52 ± 0.25) = 10.52 ± 0.25

Comparisons using power-law fits yield similar results: Coma Comparisons using power-law fits yield similar results: Coma and field LFs very similar with field somewhat flatter. Land field LFs very similar with field somewhat flatter. L**

virtually the same for field and Coma.virtually the same for field and Coma.

**(L(L**(IR)) is ~45x higher in Coma than in the field(IR)) is ~45x higher in Coma than in the field

**(L(L**(R)) is ~63±15x higher in Coma than in the field(R)) is ~63±15x higher in Coma than in the field

=> Coma IR LF not markedly different than field LF.=> Coma IR LF not markedly different than field LF.* * (Perez-Gonzalez et al. 2005); incompleteness may flatten faint end (Perez-Gonzalez et al. 2005); incompleteness may flatten faint end slopeslope

13

LF in Different LF in Different Cluster RegionsCluster Regions

LF does not vary LF does not vary strongly with location strongly with location in the cluster (but in the cluster (but beware of small no. beware of small no. statistics).statistics).

Cluster core does Cluster core does appear to be deficient appear to be deficient in both very low and in both very low and very high luminosity very high luminosity galaxies compared galaxies compared with the outer with the outer regions.regions.

All galaxies with All galaxies with LLIRIR>10>104444 erg/sec lie erg/sec lie outside the core.outside the core.

14

LF as Function of Galaxy TypeLF as Function of Galaxy Type

• Spirals dominate Spirals dominate bright end, E/S0 the bright end, E/S0 the faint endfaint end

• Spiral Spiral =1.17±0.25 =1.17±0.25 same as Pozzi et al. find same as Pozzi et al. find for field spirals (1.10 for field spirals (1.10 ±0.25)±0.25)

• Early-type galaxies Early-type galaxies contribute only about contribute only about 15% of the surface 15% of the surface density but are very density but are very important for L<10important for L<104343 ergs/sergs/s

15

Extended Dust EmissionExtended Dust Emission

Recall possible ISO detection of 0.1 MJy/sr at Recall possible ISO detection of 0.1 MJy/sr at 120120mm

Looking at fluxes after subtraction of galaxies and Looking at fluxes after subtraction of galaxies and smoothing to ISO resolution, MIPS sets limits ofsmoothing to ISO resolution, MIPS sets limits of– 2424m: <.002 MJy/srm: <.002 MJy/sr– 7070m: <0.1 MJy/sr (need to be careful of m: <0.1 MJy/sr (need to be careful of

foreground cirrus) foreground cirrus) Dwek et al. 1990 predictions for dust heated in hot Dwek et al. 1990 predictions for dust heated in hot

x-ray emitting gas:x-ray emitting gas:

2525m ~ 0.5 kJy/srm ~ 0.5 kJy/sr

6060m ~ .050 MJy/srm ~ .050 MJy/sr

So MIPS limits support Dwek’s calculationsSo MIPS limits support Dwek’s calculations

16

ConclusionsConclusions The Coma LF is similar to the field LFThe Coma LF is similar to the field LF

– SFR not strongly dependent on environmentSFR not strongly dependent on environment Within the cluster, we find evidence that the SFR is Within the cluster, we find evidence that the SFR is

dependent on environment with the lower density portion dependent on environment with the lower density portion of the cluster containing the most luminous galaxiesof the cluster containing the most luminous galaxies– consistent with cluster core galaxies losing some fraction of their consistent with cluster core galaxies losing some fraction of their

ISMISM Lowest luminosity galaxies have masses below the Lowest luminosity galaxies have masses below the

threshold suggested for effective stripping (Mori and threshold suggested for effective stripping (Mori and Burkett) which suggests that some other effect reduces Burkett) which suggests that some other effect reduces the critical mass for strippingthe critical mass for stripping

Global SFR is ~0.8 MGlobal SFR is ~0.8 M /yr/yr

SFR for core 8.5 MpcSFR for core 8.5 Mpc22 is 213 M is 213 M /yr/yr Extended dust emission neither confirmed nor ruled outExtended dust emission neither confirmed nor ruled out

17

More Checks on 24More Checks on 24m to Luminosity m to Luminosity ConversionConversion

Derived Derived luminosity luminosity does not does not depend on depend on which color which color is used.is used.

18