Only Mostly Dead The new story of Early-Type Galaxies

“Mid- to Far-IR Emission and Star Formation in Early- Type Galaxies”, Young et al., 2009 AJ

Star Formation across the Spectrum

 1988-D. Walsh, G. Knapp et al.: Far-IR/ Radio in some S0s comparable to spirals  2004-Fukugita et al.: H-alpha emission present, but no AGN  2007-Schawinski, Kaviraj: GALEX era provides new investigation of galactic CMD

5 – 30% early types are forming -1 stars, ~tenths Mo yr

Science Motive

 Kennicutt-Schmidt relationship: gas surface density relates to star formation  MIR emission (24 μm) in stellar photospheres, CS dust, dust lanes/disks, AGN and star formation  In molecule poor (CO) Early Types, 24 μm emission follows nuclear sources, photospheric light, or CS dust. In CO-rich, emission is extended, why?

How does Young interpret 24 μm emission?  Point-like?  AGN  Trace stellar light ?  CS dust  Trace Molecular Gas?  Star formation

Observations

Distances in references, Optical photometry (B-band ?); V,I WIYN and KPNO [van Zee, authors reduced], 20 2 -1 -1 H2 mass from scaling CO/H2 (3.0x 10 cm (K km s )

Spectral Coverage outside of the IR:  1.45GHz Radio Continuum-Lucero and Young 2007, FIRST (Becker et al. 1995)  Partial coverage g and i – SDSS  Partial F606W or F555W - HST ACS  H I emission survey – VLA

Spitzer Obs.

 MIPS – 24, 70, 160 μm (3 Progs.)  Processed for:  Droop Correction  Non-linearity in ramps  Non-linear, statistical outliers  Final Mosaic with 1.5” pixels  Additionally, 70/160 μm processed for stim flash corrections  Opting not to use sTinyTim, Empirical PSFs were derived from archived photometry  24 and 70 μm -- Bl Lac, 3C273, 3C279  160 μm -- unresolved SINGS galaxy, Mrk 33

Results  70, 160 μm images too unresolved for a morphological analysis  24 μm only used for analysis, and images were fit with Bendo (2006) techniques to characterize flux and dust emission

Editorialized: Three classes

UGC 1503, NGC 4526, NGC 4459  Class 1  Strongly Suggestive of ongoing Star Formation  No evidence of AGN  Class 2  Mildly Suggestive NGC 4476, NGC 3032,  Evidence of Interactions  Environmental Effects NGC 3656, NGC 807  Class 3  Red and Dead  AGN present  Misclassified NGC 5666, NGC 2320

Class 1 – UGC 1503  Evidence:  Central “Mottling”  Regularly rotating Molecular Disk  Coincident with Radio Continuum emission  Arguments:  If 24 μm traced starlight, then it would not be double peaked  If old stellar population, radio coincidence requires another argument

Class 1 – NGC 4459  Evidence:  Regular rotating molecular disk  Compact disk (central) ~ 80% 24 μm flux  Similar sized radio continuum disk and inner dust ring  Arguments:  Maybe Exp. disk is CS dust, but the interior emission is matched with optical results suggesting star formation (?)  Sarzi et al. 2005---ionized gas disk, low [OIII]/H  Kuntschner et al. 2006, Emsellem et al. 2004—young, dynamically cold gas disk  Can’t rule out AGN on morphology arguments

Class 1 – NGC 4526

 Evidence:  Radio Continuum matches molecular gas  24 μm within exponential disk  Arguments  Similar to NGC 4459, sans AGN concerns

Class 2 – NGC 4476

 Evidence:  F475W shows numerous point sources  24um follows CO morphology  Arguments:  Interacting (ICM stripping), no radio continuum  GALEX: UV color index -~1.2 mag (r < 12”), ~2.5 mag (large r)

Class 2 – NGC 807

 Evidence:  Plateau-ed 24um doesn’t follow stellar light, is too broad to be AGN  24um follows CO morphology  Arguments:  Presence of nuclear point suggests point source present  Symmetry is too clean

Class 2 – NGC 3032

 Evidence:  Arguments  Radio Continuum elongated along stellar  Counter-rotating disk w/r/t stellar rotation and dust disk  J-band (2MASS): 85% in r1/4 profile out to 85”  Line Ratios and stellar line ratios (Sarzi and Kuntscher) consistent with line ratios

Class 2 – NGC 3656

 Evidence:  Arguments  Radio Continuum matches molecular gas  An Early Type? matches 24 μm emission  Shells  Rings  Arms

Class 3 – NGC 2320

 Evidence:  Arguments  Difference in J and 24um emission scales  AGN present?  Bright elongated blue disc  Molecular gas has a tail  No knowledge of the ionization state of the gas, dynamic state of molecular gas

Class 3 – NGC 5666

 Evidence:  Arguments  Distinct lack of 24 um emission at center  Is this an Early Type?  Peak and extent of Radio C. and 24 um are  There’s at least one arm in the NW common  Blue star-forming knots

Corroboration

 NIR + MIR  Problem:  Temi 07,08 CO poor ellipticals finds 24 μm emission traces J Band emission  Y08: 24 μm is bounded by bright J band regions  Solution: CS must outshine the SF  Mean 24 um/K band factor of 15 greater than Temi  Extended 24um emission of N4459 and N4526 are consistent with Temi GUIDE: General population of CO-rich ellipticals Temi (CO poor) with crosses and spirals (?) Y08 with squares Solid line: general relationship for ellipticals Dotted line: Guideline for Y08 population

Corroboration  FIR + Radio  Yun 01:  Population of 1809 galaxies across Hubble Sequence q > 2.34 star forming  < 1% of population are FIR excess  FIR Excess emission motivated by enshrouded AGN or compact nuclear starbursts (“hot” [60-100 um] dust) or evolved stars (“cool”)  Y08: (small number statistics)  85% of galaxies satisfy q criteria  ~15% (small number statistics) of sample are FIR-Excess  SF candidates all fall into “cool” dust category  Future Work GUIDE: General population of CO-rich ellipticals  Why is the radio continuum so weak? YRC: crosses  Weak fields from cluster Y08: Circles, Large Arrow (size represent stripping? error?)  Draine ’07: FIR emission from ISM-not Temi: Triangles, Small Arrows SFRegions

Convalescence

SFR estimated from Calzetti 07: M Dynamical Timescales τ = H −1= × − 38µ 0.885 SFR( Msun yr ) 1.27 10 ( L (24 m )) SFR

Dynamical Scales “comparable” between Es and S0s,

Conclusions

Conclusions

 Young’s primer on Star Forming Ellipticals  Get as broad a spectrum baseline as possible and correlate, correlate, correlate!  CO emission maps will show cold gas (Schmidt Law input)  Radio Continuum can reveal star formation  24 um will show CS dust OR recent star formation  K band “excesses” can reveal bright hot stars (indirectly) which can drown out CS dust signal  FIR (50-150 um) can provide “cold” vs. “hot” dust information, in conjunction with FIR+Radio Yun diagnostic can reveal AGN or starbursts or maybe just old stars  Polarization maps can reveal young stellar sources (or at least the recently dead ones)  (Produce broadband optical SEDs-a sprinkling of blue stars can “ruin the whole bunch”)

 What can SF Ellipticals do for you?  Disentangle the FIR-Radio Star Formation relationship  Provide simple labs for understanding  Magnetic Fields in the ISM  Cluster Stripping  hierarchical assembly  Schmidt paradigm

The Fork’s still Tuned SINGS’ Hubble Sequence

“Variations in 24-μm morphologies among galaxies in the SINGS: new insights into the Hubble sequence” Bendo et al., 2007 MNRAS

Introductory Insights

“Early-type galaxies are generally found to be compact, centralized, symmetric sources in the 24-μm band, while late-type galaxies are generally found to be extended, asymmetric sources.”

“These results suggest that the processes that increase the real or apparent sizes of galaxies’ bulges also lead to more centralized 24-μm dust emission.”

“However, the 24- μm morphological parameters for the galaxies in this sample do not match the morphological parameters measured in the stellar wavebands.”

The Dataset

SINGS team

Morphological Parameters  Concentration Parameters r  C Small  Centralized Emission  Central Concentration, C: Bershady, = 80 Jangren, and Conselice 2000 C 5log   r20  C Large  Diffuse, Extended Emission

 M  M more negative  Centralized Emission Central Concentration, M20: Lotz = 20 20 M 20 log   2004 M tot  M20 less negative  Extended Emission

R R large  IR extended w/r/t starlight  IR Concentration, R : this paper = IR e eff R e Ropt Re small  IR compact w/r/t starlight

 Morphology Parameters

∑ f(,)(,) i j− f i j 180 A large  asymmetric emission  Asymmetry, A: Abraham,1996 A = i, j ∑ f(,) i j Warning: Center dependent!! i, j

1 n G small  smooth emission  G=∑ (2 i − n − 1) f ( i ) Gini Coefficient, G: Lotz,1994 − f n( n 1) i= 1 G large  peaky emission

Robustness Tests  Variability with distance  Q: If you re-project galaxies at greater distances, is morphology affected?  A: Moderate effects in 3.6 μm images, particularly A of Irregular Galaxies  A varies by 2 for all galaxies at 24 um

 Variability necessitates re-calibration

Re-project all galaxies in sample and calculate A at each distance

Robustness Tests  Variability with Inclination  Q: If you re-project at a different inclination, does it affect the morphology?  Re-projected on a plane at angles between 0-80o  “For this analysis, the emission is assumed to be infinitely thin, although we note that significant stellar emission may extend outside the plane of S0 and early-type spiral galaxies.”  Reff and C vary

 Variability necessitates re-calibration

Re-project all galaxies in sample and calculate C at each Angle

Variation by Hubble Type

Symmetric Asymmetric

Smooth Peaky Extended Centralized Do Bars beget Stars?

24 μm morphology differs between galaxies of same type due to AGN, Interactions, Gas Infall, Asymmetric rings, circum- nuclear starbursts…

Can it tell us the bar’s role in facilitating star formation?

Do Bars beget Stars?

 Conclusions:  SB more centrally concentrated at 24 μm  SB more peaky in emission  Results significant to 3σ only for full sample, biased by late types  Bars may play a role, but larger sample set must be explored

Discussion – disordinate parameters  “Starlight” Morphologies

Lotz et al. 2004: (Restframe 6500 Å, 4400 Å ULIRG study) Bendo et al. 2007 (this work): 3.6 μm – open dots Circles-E/S0, Triangles-Sa-Sbc, Crosses-Sc-Sd, Stars- ULIRGs (11.5 < log(L /L ) < 12.5), Bars-Edge On Spirals 24 μm – filled squares FIR Sun

Discussion - disordinate parameters

 “Starlight” Morphologies

Bendo et al. 2007 (this work): Conselice et al. 2003 (CAS R-band study): 3.6 μm – open dots 24 μm – filled squares Hexagons – cDs/S0, Filled Squares-Early Type Spiral, Stars-Late-Type Spirals, Starburst-Irregulars, Point-dE, Open Squares-Starbursts, Open Dots-ULIRGs (L>1011 LSun)

Discussion  Dust and ISM Morphologies  Dust variations are present in similar distribution regardless of wavelength  claim: single wavelength can be used to understand galactic distribution  Dust emission more centrally located in early type Spirals  v.v. Young et al. (1995)  Variations in H II region radial distribution (Hodge and Kennicutt 1983) similar to 24 μm spatial extent  But differs from Dale et al. 2001 (cluster vs. field?)

 Reff,24μm relates (weakly) to morphology  Similar to Young morphology-CO relationship  To be expected: CO traces gas mass, so too does 24μm emission

 Interpreting Hubble Morphology  Star/Bulge formation theories (all of them) validated  Unequal mass mergers produce larger bulges  Ram pressure stripping strangles disc star formation, bulge dominates light  Pseudo-bulges (galactic funnel mechanisms)  All scenarios imply larger bulges for earlier galaxies

Discussion

 Dwarf Galaxy interpretations  Confirmed: Dwarf galaxies are still weird  Amorphous morphology  Peaked, Non-Peaked  Asymmetric morphologies

Conclusions

 Statistically significant 24 μm variations occur along the Hubble Sequence  Earlier types tend to be more symmetric, more centralized, less clumpy  Supports galactic evolutionary theories  Bars enhance concentration in 24μm  Suggests star formation is enhanced by bars  24 um matches trends in optical  Caution: ULIRGs and Starbursts reside in similar parameter space with 24 um galaxies  Gas and Dust trends in Hubble Sequence re-iterated  Caution: 24 μm emission profiles do not support previous work which find no trend in HI distributions with Hubble type