1 / 42

Star formation and stellar populations at the peak era of galaxy growth

Star formation and stellar populations at the peak era of galaxy growth. Mark Dickinson (NOAO). Cosmic. Cosmic High Noon: the peak epoch of star formation, 1 <~ z <~ 3( ish ) .

kathy
Download Presentation

Star formation and stellar populations at the peak era of galaxy growth

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Star formation and stellar populations at the peak era of galaxy growth Mark Dickinson (NOAO) IAP-Subaru meeting

  2. Cosmic

  3. Cosmic High Noon: the peak epoch of star formation,1 <~ z <~ 3(ish) Accurate estimates of star formation rates and stellar masses are essential if we want to understand the physics of galaxy assembly. Derived SFR(z) may overproduce derived *(z) at most redshifts. SFR(z) Wstars(z) Hopkins & Beacom2006

  4. Stellar populations at cosmic noon We need accurate measurements of star formation rates and stellar masses at the peak epoch of galaxy formation, both for an accurate “census” of the SF history and to understand the physics of galaxy formation and evolution. Many challenges, including: • SFRs: • Most energy from star formation is absorbed & reradiated by dust • Uncertain IR bolometric corrections from observed wavelengths • Understanding contributions from AGN • Measuring the faint end of the SF distribution function • Stellar masses & populations: • Stellar population models • Strong and uncertain extinction • Metallicity dependences and evolution • “Overshining” and the past SF histories of galaxies • Completing the census to low masses • Reliable identification of evolved or dusty galaxies at z >> 2 • Everything/everywhere: • IMF? What is it, does it vary with environment, conditions, metallicity, time…

  5. Some challenges for measuring high-z star formation • UV alone will always miss dusty star formation, and requires large corrections which must be verified and which are unlikely to be universally correct • IR alone has not yet been sensitive enough to detect most of the star formation at z >> 1 (and very little at z >> 2).

  6. GOODS-Herschel PI: David Elbaz (CEA) Deepest images of the sky in the 2 GOODS fields : ~1800 sources down to 1 mJy at 100 mm, 2.6 mJy@160mm, 6 mJy@250mm, 7 mJy@350mm, 9 mJy@500mm Full data release coming soon! GOODS-North GOODS-South 100160 250 24100160 10'x16' 10'x10'

  7. GOODS-Herschel: Daring to detect the ordinary! GOODS fields are unique for PACS and SPIRE 250mm data deep enough to detect ~L*IR galaxies at z ≈ 2 L*IR = 7 x 1011 Lo @ z≈2 (Magnelli et al. 2011) L*(IR) vsz. Magnelli et al. 2009, 2011

  8. Pre-Herschel: Papovich et al. 2007, Daddi et al. 2007; Magnelli et al. 2009 Does 24mm data overestimate LIR at z ~ 2 ?(a.k.a. the mid-IR excess problem) z ≈ 2 Elbaz et al. 2010, 2011 Nordon et al. 2010 z ≈ 2

  9. Focusing consistently on L(8mm) vs. L(IR) changes the picture Elbaz et al. 2011 IR8 = L(IR) / nLn(8mm) CE01 template extrapolation from 24mm -> L(IR) No template extrapolation: z ~ 0: IRAC 8mm z ~ 1: IRS 16mm z ~ 2: MIPS 24mm Starburst population

  10. Noeske et al. 2007 AEGIS 0.2 < z < 1.1 Brinchmann et al. 2004 SDSS z ~ 0 Daddi et al. 2007 GOODS z ~ 2 M. Dickinson - NMSU

  11. Starburst galaxies have: • High SSFR • High SFR surface density • Larger 8mm bolometric correction (IR8) z ≈ 0: L(IR) vs. L(8mm) LIRGs with compact / high surface brightness star formation from GOALS (Díaz-Santos et al. 2010) z ≈ 0: SFR vs. M*

  12. New IR templates from GOODS-H Constructed by shifting normalized GOODS-H photometry to the rest frame

  13. New IR templates from GOODS-H Constructed by shifting normalized GOODS-H photometry to the rest frame

  14. Challenges deriving SFR(IR) at high redshift 24mm @ z≈2 There is significant and systematic variation in the mid-IR bolometric correction. This makes it very difficult to universally estimate LIR or SFR from Spitzer 24mm data alone at z > 1.5 without additional information about the nature of the galaxies observed. It is hard (impossible?) to know if a galaxy is “MS” or “SB” from mid-IR or UV data alone.

  15. Even the deepest Herschel data barely reach ~L*(IR) at z ≈ 2 • Direct measurements of far-IR emission at lower luminosities require stacking, lensing, etc. • ALMA is far more sensitive, but (1) cannot survey much sky area, and (2) submm bolometric corrections are themselves uncertain L*(IR) vsz. Magnelli et al. 2009, 2011

  16. Challenges for evaluating stellar populations and masses • Spitzer IRAC achieved sensitivity needed to detect most of the mass density at z < 5(ish) • However, photo-zs and SED fitting at z > 1 benefit from extremely deep near-IR (and optical) data, often hard to achieve • Extremely dusty galaxies • Very high redshift galaxies (this morning’s talks) • HST WFC3-IR, UltraVISTA, VLT/HAWK-I… • Extreme extinction for high-z galaxies may influence or bias derived stellar population properties

  17. CANDELSCosmic Assembly Near-infrared Deep Extragalactic Legacy Survey Co-PIs: Sandy Faber (UCSC) and Harry Ferguson (STScI) with a cast of thousands (well, 100+ scientists, 12+ countries) • HST WFC3-IR J+H imaging of regions within 5 important deep survey fields (GOODS-N+S, COSMOS, UDS, EGS) totaling ~900 arcmin2 • Very deep Y+J+H imaging of two regions (135 arcmin2 total) within GOODS-N+S • Overlapping ACS parallels, mainly in V606 + I814 • WFC3-UVIS ultraviolet observations in GOODS-N (only) • Multi-epoch observations to identify SNeIa out to z ~ 2 • Survey is more than half complete • 16 public data releases so far via MAST • Follow the CANDELS blog! • http://candels-collaboration.blogspot.com/

  18. CANDELS WFC3-IR imaging of Herschel ULIRGs at 1.5 < z < 3 Kartaltepe et al. 2012 • CANDELS WFC3-IR data provide: • High resolution optical rest-frame morphology • Very deep near-IR photometry • Matches sensitivity of IRAC and optical photometry • Valuable for SED-fitting, photo-z’s

  19. CANDELS+Herschel M.Dickinson, D. Elbaz et al. Extending GOODS-depth Herschel imaging to the CANDELS COSMOS and SXDF/UDS fields PACS (100, 160 mm) and SPIRE (250, 350, 500 mm) First data, hot off the telescope: CANDELS-COSMOS

  20. UV extinction and reddening At high redshift, the UV remains the most sensitive means to measure star formation, but is strongly attenuated by dust. Meurer et al. 1999: IRX-b relation for local UV-bright starburst galaxies Close correlation between the FIR/UV flux ratio (total UV extinction) and the UV spectral slope b (UV reddening)

  21. Local IRX-b Goldader et al. 2002 Local ULIRGs (very high SSFRs) fall well above (or left) of the Meurer relation Kong et al. 2004 Local spirals (relatively low SSFRs) fall below (or right) of the Meurer relation

  22. Reddening and extinction at high redshift Reddy et al. 2010: Spitzer 24mm-based IR luminosities vs. UV Typical UV-selected galaxies (LBGs) at z≈2 roughly follow the local IRX-b relation The most IR-luminous LBGs (ULIRGs) deviate, similar to locally (Goldader+2002) Typical LBGs at z≈2

  23. Verification with Herschel Reddy et al. 2012: 100mm and 160mm stacking confirms the Spitzer-based result on average

  24. Dust attenuation in IR-luminous galaxies, 1 < z < 2 Buat et al. 2012: UV to IR SED modeling (CIGALE) for UV-selected galaxies, 0.95 < z < 2.2, with Herschel and Spitzer detections Overzier+2011 (local) Buat+2012 (1 < z < 2) Herschel PACS Spitzer 24mm only

  25. Systematics in UV attenuation • Attenuation properties depend on IR luminosity and stellar population age • Relatively little dependence on specific star formation rate (MS vs. SB), at least for this sample Main Sequence 1 < z < 2 Buat et al. 2012

  26. A variety of dust attenuation behaviors at high z? Different samples, redshifts, and analyses have yielded different results Buat et al. 2012: mostly 1 < z < 2 Herschel+Spitzer Murphy et al. 2011: mostly 0.66 < z < 1.5 Spitzer 24mm+70mm,

  27. Extreme extinction at z≈2 Dey et al. 2008: Dust Obscured Galaxies (DOGs), f(24mm) / f(0.65mm) > 1000 Penner et al. 2012: Herschel PACS+SPIRE observations of DOGs in GOODS-N

  28. DOGs have unremarkable mid/far-IR colors but very red UV/optical colors 100mm / 24mm R - K

  29. DOGs have unremarkable specific SFRs (and morphologies, see Kartaltepe et al. 2012, Schawinski et al. 2012)

  30. DOGs are just very dusty…

  31. What if the attenuation curve looked like this … J. Pforr in prep. (see also Pforr et al. 2012) Attenuation curves cooked up to match various UV attenuation & reddening relations Changes mainly in the blue, with red/near-IR attenuation roughly fixed (in most cases) Calzetti DOGs Murphy

  32. SED fitting for extremely dusty z≈2 galaxies Very deep CANDELS/GOODS photometry important to measure the Balmer break and UV rest-frame slope J. Pforr in prep.

  33. Effects of modified attenuation on zphot and M/L J. Pforr et al. in prep. • For extremely dusty objects, how much does the assumed reddening law affect derived stellar masses? • Fitting CANDELS photometry for DOGs in GOODS-S • Typically: • <D log M/L> ≈ 0 • s(log M/L) ≈ 0.1 dex • -> Fairly radical modifications of the attenuation law in the blue/UV have only modest impact on derived M/L, although photo-z’s can scatter. “DOG-like” Low RV High RV “DOG-like” “Murphy-esque””

  34. The spread in the main sequence at z≈1 Salmi et al. 2012: SFRs from 24mm + UV; stellar masses from SED fitting Offset from MS average depends on disk color and clumpiness Disks: n < 1.5 More bulge: n > 1.5 Much of the spread in the MS is due to real, physical effects, not measurement uncertainties (see EmanueleDaddi’s talk tomorrow)

  35. The spread in the main sequence at z≈1 Salmi et al. 2012 • slope = 0.983 • = 0.139 “Correcting” the MS residuals for color and clumpiness leaves a very tight, nearly linear relation This suggests that (non-systematic) uncertainties in derived SFR and M* estimates are < 0.1 dex

  36. Cosmic SFR-history, revisited • Consistent combination of IR- and UV-derived SFRs from the best current data sets gives relatively good consistency between SFR(z) and W*(z) for conventional IMF. • Caveats: • very little statistical information on dusty SF at z >> 2 • stellar mass census may be quite incomplete at z >> 2 Salpeter IMF Madau & Dickinson in prep.

  37. Not everything at z >> 2 is dust-free Williams et al. 1996: HST optical Hughes et al. 1998: SCUBA 850 mm

  38. Not everything at z >> 2 is dust-free Williams et al. 1996: HST optical Hughes et al. 1998: SCUBA 850 mm

  39. HDF 850.1: a hyperluminous IR galaxy in a protocluster at z=5.183 F. Walter et al. 2012, Nature SFR ≈ 850 Mo/yr

  40. Summary • Reliably estimating star formation rates and stellar masses from photometric data at high redshift would seem to be fraught with peril, but empirically there seems to be hope! • Far-infrared measurements (esp. Herschel) have been essential to understand and derive dusty SFRs at z > 1 • Spitzer 24mm detects more sources, but systematics in bolometric corrections make it difficult to derive SFRs universally (e.g., MS vs. SB) • Extremely deep NIR photometry is essential for a thorough census of stellar masses at high redshifts • Dust extinction and reddening laws are not universal and depend on galaxy properties • Another reason to worry about SFRs derived from UV alone without far-IR • Reassuringly, stellar mass estimates appear to be fairly robust, even for objects with extreme extinction • Dispersion in the star-forming main sequence at z~1 is in part due to physical properties of galaxies • Suggests that measurement accuracy of SFR and M* is < 0.1 dex • Not all star formation at z >> 2 takes place in low-extinction environments!

  41. Thank you Nobuo for giving us such a great excuse to come to Paris!

More Related