Galaxy Build-up from Far-IR Perspective. Amy Barger

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1 Galaxy Build-up from Far-IR Perspective Amy Barger

2 Very luminous galaxies emit most of their light at IR to mm wavelengths We miss galaxies in the rest-uv selection because they are faint And we underestimate the bolometric luminosity corrections for the galaxies that we do see in the rest-uv IRAC Figure from Polletta MIPS SCUBA-2 HERSCHEL

3 GN20; Pope et al. 2005, Hodge et al GOODS850-5; W.-H. Wang et al. 2004, 2007, 2009 Where emission is seen in the higher redshift galaxies, it generally lies outside the main part of the galaxy 10 HST F450W, F814W, F160W White square = centroid from SMA White contours = VLA 20 cm CO redshifts from Daddi et al. 2009a,b and Walter et al GN20.2; Pope et al HDF850.1; Hughes et al. 1998

4 Ways of constructing large, uniform samples of highredshift luminous, dusty galaxies 5-20 cm imaging (VLA, etc) Advantages: wide field, high resolution Disadvantages: biased against high redshifts, contaminated by AGN Need an order of magnitude increase in depth for ULIRGs at z=6 X-ray AGN, L X >10 42 erg/s X-ray quasars, L X >10 44 erg/s Deepest 20 cm image (5σ=11.5 µjy) of CDF-N by F. Owen

5 Single-dish submm/mm imaging (Herschel in space; JCMT, LMT, APEX, IRAM, SPT, etc, on the ground) Advantages: large fields, uniform FIR/submm selected samples, sensitive to very high redshifts, particularly in the longer wavelength ground-based observations Disadvantages: low resolution, confusion limit for blank fields 0.8 FWHM Not confusion limited. Integrating longer can detect fainter sources. 15 FWHM Confusion limited. Integrating longer can NOT detect fainter sources.

6 Red colors [KIEROS: K 4.5 micron > 1.6 (W.H. Wang et al. 2012); HIEROS: H 4.5 micron > 2.25 (Caputi et al. 2012; T. Wang et al. 2016); red colors in optical/nir (Chen et al. 2016) Advantages: large fields Disadvantages: biased to high redshifts where the K-band becomes fainter Radio sample in CDF-N Cowie et al. 2016

7 Interferometric submm/mm imaging (ALMA, IRAM PdB, SMA) Advantages: high spatial resolution and sensitivity Disadvantages: very small field-of-view Dunlop et al (16 sources > 120 microjy at 1.3mm); Walter et al survey contained within

8 Exploit Strengths of Different Types of Observation Use single-dish far-infrared/submm imaging to construct large samples of far-infrared selected sources Use the radio to obtain precise positions, sizes, and redshift estimates Use submm interferometry to identify interesting cases where there is no radio identification, or where there is more than one possible radio counterpart, and to make sure the flux is not from multiple galaxies In addition, use Chandra/XMM to identify X-ray AGN

9 SCUBA-2 >250 hours (band 2) on the CDF-N/GOODS-N and CDF-S/ GOODS-S fields to probe below the confusion limit of 2 mjy at 4 σ

10 SCUBA-2 image deeper than SCUBA image of HDF-N over 120 arcmin 2. Homogeneous, cleanly selected, well calibrated: sigma sources SCUBA (Hughes et al. 1998) SCUBA-2 (Cowie et al. 2016)

11 Many of the CDF-N SCUBA-2 sources have radio counterparts, but if relied only on radio for positions, ambiguity when multiple radio sources 20 cm contours overlaid on HST F140W images centered on SMA positions Barger et al Radio data from Owen 2016

12 Interferometric Submillimeter Follow-up Blue: SCUBA-2 > 2.5 mjy Gold: VLA Red: SMA (CDF-N) or ALMA (CDF-S; PI Bauer for SCUBA-2 follow-up, but also sources from PI Aravena and PI Mullaney and ALESS survey; 83 total)

13 When Visible in B,Z,H, ALMA Detections a Pretty Red Bunch!

14 ALMA ALESS Survey in CDF-S LABOCA (LESS; Weiss et al. 2009) was used to survey the CDF-S, and ALMA was used to follow-up the sources (ALESS; e.g., Karim et al. 2013; Hodge et al. 2013; Ian Smail talk) Deep area (<twice the central noise) in X-ray (green) for CDF-S (A)LESS missed many of the sources in the central region covered by the 7 Ms X-ray image Red = ALESS Blue = 4σ SCUBA-2

15 Interferometry Has Revealed Some Multiplicity GOODS SMA b a c ACS W.-H. Wang et al. (2011), using the SMA, was first to discover that some bright SCUBA sources resolved into multiple, physically unrelated sources (see also Smolcic et al. 2012, Karim et al. 2013, Hodge et al. 2013, etc) MIPS VLA Ks, IRAC Chandra All of the brightest ALESS sources (S 870mm >12 mjy) were found to be composed of emission from multiple fainter sources, each with S 870mm <9 mjy; no ALMA source was >9 mjy

16 Triple from a CDF-S ALMA Observation ALMA SCUBA-2 (ALMA observation from J. Mullaney)

17 But we find most bright SCUBA-2 sources are singles Scuba-2 beam Band 6 detections

18 Clustering an issue: Some of the bright CDF-N sources (there are ten > 9mJy total, 3 in this structure) lie in a single region (radio/submm flux ratio suggests z~4) GN20 Casey et al. 2015, 2016: given the short lifetimes, submm groups at a single redshift are hard to understand, since there doesn't seem an obvious way to synchronize the star formation

19 Progress Has Been Made on the Following Questions What fraction of the star formation is missed in the UV selected samples? How does the star formation rate density function evolve with redshift? Is there a maximum star formation rate (SFR) in high-redshift galaxies?

20 Observed SEDs lie within multiplicative factor of 1.8 down to 50 micron (see also da Cunha et al. 2015). Shorter wavelengths dominated by hot dust emission (extend fit with MIR power law; e.g., Casey 2012) (Elbaz et al. 2011, Magnelli et al. 2013)

21 Black: z<2 Blue: z=2-3 Green: z=3-4 Gold: z=4-5 Red: z=5-6 Redshifts can be estimated from flux ratios

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23 Converting to Star Formation Rates For z>1.2, the strong negative K-correction almost exactly offsets the effects of distance (Blain & Longair 1993) Thus, the observed-frame 850 micron flux will approximate the FIR luminosity independent of redshift The exact conversion depends on the spectral energy distribution of the source

24 Interpolation and integration gives a good mean conversion Adopting a theoretical conversion between L(8-1000) and SFR, find SFR = 143 x S(850) for a Kroupa IMF

25 Find an impressively large and relatively invariant fraction of the overall SFR density is contained in the massively star-forming galaxies, and this is true at all redshifts to z > 5 Madau & Dickinson (2014) total SFR density ~30%

26 Clear that UV selections do not find the highest starforming galaxies populations completely disjoint Curves at z=2 and z=3 from Reddy & Steidel 2009 Circles at z=2-4 and z=4-6 from SCUBA-2 Extinction corrected rest-frame UV ~500 M Sun yr -1 Submm

27 Important: only 20-30% of the submm extragalactic background light is contained in the bright (>2 mjy) galaxy population detected with single-dish submm surveys of blank fields Faint Sources ALMA surveys in general can probe the fainter flux populations

28 ...and single-dish lensing surveys help through the expansion of the source plane (reduces confusion) and through the magnification of the background sources. We need to connect the faint submm population to the UV population!

29 Is There a Maximum SFR? Given the lack of ALMA sources >9 mjy in ALESS, Karim et al. (2013) proposed a natural limit on the SFRs In the CDF-N, we have 10 SMA detections of SCUBA-2 sources with S 860µm >9 mjy, all of which are singles. In the CDF-S, we have found 2 with ALMA (CDF-N may be more representative) Red=spectroscopic, blue=photometric, green=z_250

30 We also see hints of a maximum SFR from the radio data Barger et al. 2016

31 Contributions to the SFR density have really dropped by 2000 MSun yr-1

32 The Effect of AGN on Their Hosts There is a popular theoretical picture that AGN suppress star formation in extremely high-mass galaxies (Sanders et al. 1988; cartoon from Alexander & Hickox 2012) We can look to see how dusty, massively star-forming galaxies are related to X-ray sources

33 Are there X-ray counterparts to the SMA confirmed CDF-N SCUBA-2 sample? SMA The most luminous star formers do not contain X-ray AGN

34 What are the submm properties measured from the SCUBA-2 images of the CDF-N X-ray sample? SMA The X-ray luminous AGN are drawn from lower starforming galaxies

35 Big Questions for Meeting and Beyond What fraction of the star formation is missed in the UV selected samples? How do we connect the UV selected samples with the submm selected ones? How does the star formation rate density function evolve with redshift? Does the high end of the star formation rate distribution function occur in very overdense environments? Is there a maximum star formation rate (SFR) in high-redshift galaxies? If so, can this be explained theoretically? When do the first dusty star-forming galaxies form? How is the dust produced, and how does it grow in galaxies? Is there any conflict with hierarchical structure formation? What role do supermassive black holes play in stopping the growth of their host galaxies?