Lecture 10. (1) Radio star formation rates. Galaxy mass assembly history

Transcription

1 Lecture 10 (1) Radio star formation rates (2) Galaxy mass assembly history

2 M82 radio/fir spectrum (z = 4.7) (z = 4.4) Synchrotron Free free Dust

3 Cosmic SFH: Calibration Kennicutt 1998 Ann Rev A&A 36, 189 (Salpeter IMF) UV continuum ( Å) : Pro: Extensive datasets over 0<z<6; know stellar evolutionary tracks & w/imf, # of stars in a given mass interval, so know light produced each λ Con: dust! IMF dependence 2. Line emission (Hα, [O II]) : Pro: Very sensitive probe, available to z~2 (lose in thermal IR) Con: strong IMF dependence ( 3); dust (use Balmer decrement to correct); excitation uncertainties [OII] 3. Far IR emission ( µm) : Pro: Independent method, available for obscured sources to high z: Con: uncertain source of dust heating (AGN/SF?); primarily applicable in starbursts due to detection limits at high z; bolometric FIR flux required

4 Normal Galaxies, Radio Galaxies and AGN Radio Galaxies AGN

5 Normal Galaxies, Radio Galaxies and AGN NGC1097 Radio Galaxies AGN Normal Galaxies

6 Radio Source Counts Starburst Radio galaxy/agn SKA VLA B2 3C

7 SSA GHz VLA 9/x9/

8 SKA Sensitivity HST VLA SKA

9 Far Infra Red v Radio Continuum correlation Arp220 St ar Fo rm Radio at io n Ra te Condon (1992) Galaxy FIR M82 Linear correlation over a luminosity range of 104 Dispersion 0.3 in the log Lowest dispersion of all spiral galaxy correlations

10 M82 Subaru (B,V,Hα) M82 Starburst Galaxy Direct evidence for star formation M82 VLA+ MERLIN+VLBI Radio reveals expanding supernovae Calibrates integrated radio continuum SFR

11 The FIR Radio correlation Linear correlation with <50% rms scatter Independent of galaxy type Spirals, Ellipticals, Seyfert s ( AGN), radio quiet QSO s Effect is both global and local but global is tighter FIR RC correlation has the smallest dispersion of all known galaxy correlations

12 Tightness of the correlation FIR RC correlation has the smallest dispersion of all correlations hence there is not a critical third parameter (such as mass) eg look at the starburst galaxies similar mass but FIR and radio both x CO RC correlation: both global and radial distribution ratio changes from 0.6 to 2.4 (ie more scatter than FIR RC. Allen et al argue for gas heating by cosmic rays

13 FIR Correlations with other indicators Hα Radio FIR Least scatter UV Radio Hα Radio UV Most scatter Radio Continuum

14 How does this work? (Remarkable) UV ν ν IR Dust ν IR Gas Dust V U ν Dust UV ν SN Hα ν Gas e e-ee- - Radio ν IR ν

15 Molecular clouds Stars form SN Hot stars UV Heating UV Conventional Model Warm Dust FIR High Correlation! Radio SNR ISM Shocks Part. Accl. CR CR Trans port Synchro tron Magnetic Field

16 Hot stars Molecular clouds Stars form SNR Details ISM Shocks UV Heating UV Plausible? Type SN Covering factor 11 steps final correlation 50% scatter 50/ (11)=15% scatter per step! Small scale structure Part. Accl. CR CR Trans port Warm Dust Temperature, Grain Composition FIR High Correlation! Radio Synchro tron Diffusion, Escape, Energy losses Magnetic Field

17 Radio Surveys Limits AGN SF ULIRGs LIRGs Milky Way 9 Log (FIR Luminosity) 14

18 Properties of optically bright (I<23.5) ujy radio sources <M_I>= 22.5+/ 1.5 I=23.5 (spiral) ULIRGs/ AGN LIRGs spirals

19 Star Formation Rates z z IR Radiio Halpha UV

20 Number density evolution from radio data Squares: star forming radio sources with ULIG luminosities Barger, Cowie & Richards 2000 (submillimeter source density) Kim & Sanders 1998 Sadler et al Very few star forming radio sources with ULIG luminosities locally, much more common by time reach z~1

21 Galaxies 626 Mid IR star formation estimates: Crude but very popular at the minute because of Spitzer

22 Sllva et al The proportion is a strong function of galaxy luminosity ULIG OPT LIG FIR spiral Elliptical

23 E.g. the conversion from 24 µm to total FIR luminosity depends strongly on the template spectral energy distributions used to K correct the data

24 IR luminosities in the CDFS 2635 sources with * redshifts * ULIRGs : quite rare at 0<z<1 80% completeness limit Rencontres de Moriond, March 6-12th 2005 * LIRGS: significant contribution at z>0.5 * More «normal» starbursts are not negligible neither

25 60 μm luminosity Functions Ψ(L,z)=Φ*(z) ϕ[l/l*(z), z=0] * Evolution in luminosity : αl o (1+z) L*(z) = L* Φ* L* Rencontres de Moriond, March 6-12th 2005 * Evolution in density : αd o Φ*(z) = Φ* (1+z)

26 Star formation history at z<1 Lagache et al Compilation by Hopkins Blain et al total Chary & Elbaz LIR <10 L. 11 LIR >10 L. ULIRGs LIRGs/ULIRGs dominate beyond z~0.7 Rencontres de Moriond, March 6-12th 2005

27 Galaxy Mass Assembly So we have great progress in tracking comoving star formation history but: SF density averages over different physical situations (e.g. bursts, quiescent phases) reliability of measures remains a big concern; no ideal method hard to link to theory Stellar mass assembly is in some ways a more profound measurement

28 Comparison of the FIR determined star formation with the UV determined star formation Maximal corrections for missing EBL, if at z=1 3 Directly measured FIR star formation ρ t

29 Cumulative star formation history (SFH) shows actual growth of galaxies with time Cosmic baryon density Present day stellar mass density, Cole et al. (2002)

30 Galaxy masses: what are the options? Dynamics: rotation & dispersions (only for restricted populations) Gravitational lensing (limited z ranges) IR based stellar masses (universally effective 0<z<6) K

31 Stellar Masses from Multicolor Photometry spectral energy distribution Mass likelihood function log mass Spectral energy distribution (M/L)K Redshift LK hence stellar mass M log mass

32 What if you don t know the redshift? logm Expected scatter based on photo z error distribution zspec Catastrophic errors securing photo z & masses from same photometry

33 What if you only have optical photometry? A key ingredient in the mass determination is infrared photometry which is sensitive to the older, lower mass stars; important z > 0.7 BRI vs BRIK log σ (Mopt) log Mopt MIR zspec Bundy 2006 Ph.D. thesis log σ (MIR)

34 Downsizing: SFR & Stellar Mass Density SFR/volume by mass Mass/SFR Low mass galaxies are more active in terms of SFR/stellar mass at recent times

35 Results: Stellar Mass by Morphology Comoving mass density M Mpc 3 Redshift Early result: the decline in stellar mass in late types occurs at the expense of a modest growth in that of regular spirals & ellipticals, i.e. tranformation

36 Downsizing & Star Formation Using rest frame U B color as a discriminant, a threshold stellar mass is apparent above which there is no SF Cross over mass (red=blue) also increases with z Mass threshold increases from 1011 M at z~0.3 to 1012M at z >1 Stable from field to field (V/bin~2.106 Mpc3) Bundy et al (astro ph/ )

37 Stellar Mass Assembly by Type in GOODS N/S No significant evolution in massive galaxies since z~1 Modest decline with z in abundance of massive spheroidals, most change at lower mass Bulk of associated evolution is in massive Irrs Bundy et al (2005) Ap J 634,977 2dF (h=1)

38 Caveat: Dry Mergers? Caveat: Fundamental Plane measures the ages of the stars in galaxies of different masses. Young ages are seen for stars in low mass galaxies and old ages for stars in massive galaxies..seemingly in contrast to hierarchical predictions. van Dokkum (2005) argues high preponderance of red tidal features & red mergers in local samples, coupled with a postulated increase in merger rate (1+z)m implies significant mass evolution is still possible in large galaxies: i.e. stars could be old but assembled mass could be younger via self similar merging of red sub units (so called `dry mergers )

39 Dry Mergers at High Redshift Clusters: Tran et al (astro ph/ ) Field: Bell et al (astro ph/ ) No good statistics yet on how prevalent this process is

40 Palomar K + DEEP2 Sample Palomar WIRC HgCdTe imager: 8.7 arcmin FOV DEEP2: R < 24.1; 4 fields (incl. EGS, can test cosmic variance) 12,121 DEIMOS redshifts z<1.5 with K<20.0 (1.5 deg2) Goal: explore role of star formation & environment on mass assembly Star formation indicators: (U B)0 from CFHT photometry [OII] equivalent width, DEIMOS spectra (z > 0.7) Environmental density: Use nth spectroscopic neighbor diagnostic with DEEP2 redshifts (Cooper et al 2005) Bundy et al (astro ph/ )

41 Summary Techniques are now well established for estimating the stellar masses of galaxies to high redshift; reliability depends on having spectroscopic redshifts and long wavelength data It is now clear that mass assembly since z~2 does not proceed hierarchically; growth is suppressed in high mass systems at early times continuing in low mass systems to z~0 (`downsizing ) AGN feedback may be able to reproduce this behavior in ΛCDM models, but further work is needed to understand environmental dependence of this process: are downsizing trends occurring at a different rate in clusters vs `field? Massive galaxies are now being found at z>2 in surprising numbers; many are already passively evolving. This implies much SF activity at higher redshift

42 End