Deep Keck Spectroscopy of High-Redshift Quiescent Galaxies

Transcription

1 Sirio Belli Max-Planck Institute for Extraterrestrial Physics Deep Keck Spectroscopy of High-Redshift Quiescent Galaxies with Andrew Newman and Richard Ellis

2 Introduction Schawinski et al red sequence z ~ 0 blue cloud I will focus on massive quiescent galaxies

3 The size evolution van der Wel et al Quiescent galaxies are smaller at higher redshift Star-forming galaxies are larger than quiescent galaxies

4 The formation of massive galaxies (figure adapted from Toft et al. 2014) 0 redshift star-forming galaxy red nugget local elliptical How do compact quiescent galaxies grow in size? What is the physical process responsible for quenching? What are the properties of the progenitors of compact quiescent galaxies?

5 What did this galaxy look like 8 Gyr ago? this is the average evolution of galaxies: z = 2 z = 1 z = 0? Evolution of population Evolution of individual systems

6 Is the size evolution an illusion? z = 2 physical growth? no physical growth + newly quenched galaxies z = 0 Very open debate: Taylor et al Newman et al Carollo et al Poggianti et al Damjanov et al. 2013,14,15

7 How can we link galaxies? Fixed stellar mass (e.g. Daddi et al. 2005) Patel et al Fixed number density (van Dokkum et al. 2010, Patel et al. 2013) Abundance matching (Behroozi et al 2013, Marchesini et al. 2014) (a) Cumulative number density of galaxies at a given stellar mass for d These methods are based on photometric data

8 Galaxy spectra contain a wealth of information age in Myr: Cabanac et al. 2002

9 Absorption lines tell us about the stellar component The width is due to the relative motion of the stars 1 Velocity dispersions The depth is determined by the type of stars 2population Stellar properties

10 Velocity dispersion is a stable property dry merger of two identical systems on a parabolic orbit: 2 2 (M i, i)! (M f, f ) virial theorem + conservation of energy: 1 2 M i 2 i M f =2M i f = = 1 2 M f 2 f i log [ σ(z)] [km s -1 ] log [ M (z)] [M ] Hopkins et al max variation < 20% max variation: factor of z 3 see also Nipoti et al. 2003, Hilz et al log [ M (z)] [M ]

11 Evolution at fixed velocity dispersion z = 2 z = 1 z = 0 σ = 302 km/s σ = 295 km/s σ = 305 km/s

12 Absorption lines tell us about the stellar component The width is due to the relative motion of the stars 1 Velocity dispersions The depth is determined by the type of stars 2population Stellar properties

13 How to find the progenitors z = 2 z = 1 z = 0 SFH SFH Δt = 2.5 Gyr Δt = 8 Gyr

14 Archaeology at high redshift z = 2 z = 1.5 z = 1 observed at z = rest frame wavelength (angstrom)

15 Chasing red light CCD LRIS-R (2010) photographic plate visible MOSFIRE (2012) z = 0 z = 1 z = wavelength (micron) Finally, rest-frame optical lines at high redshift! e.g. van Dokkum et al. 2009, Kriek et al. 2009, Newman et al. 2010, Toft et al 2012, van de Sande et al Bezanson et al Whitaker et al Onodera et al. 2015, Mendel et al. 2015, Newman et al HAWAII-2RG

16 Entering the redshift desert Cimatti et al z = 1.7, 34.4 hours in optical z = 2.09, 8.3 hours in the near-infrared rest-frame wavelength

17 The Keck sample z = z = z = z = < z < z = z = z = z = z = z = z = z = MOSFIRE 1.5 < z < 2.5 G b H and γ H δ z = H ε LRIS z = II H ] 1 H1 1 H0 9 H 8 C a C H a K 4750 z = [O z = z = z = z = z = z = z = z = z = z = z = z = z = z = z = z = z = z = Rest frame wavelength (angstrom) Rest frame Rest frame wavelength (angstrom) wavelength (angstrom) Fig. 2. Observed LRIS spectra of the 56 quiescent galaxies for which accurate velocity dispersions were measured, sorted by redshift. The spectra are inverse-variance smoothed with a window of 21 pixels, corresponding to 7.5 A in the rest-frame (and 16.8 A in the

18 The Keck sample LRIS 1 < z < 1.5 Belli et al. 2014a, galaxies MOSFIRE 1.5 < z < 2.5 Belli et al. 2014b, 2016 in prep. 21 galaxies CANDELS fields 3-10 hours per mask ~25 Keck nights

19 The rest-frame UVJ diagram 2.0 LRIS MOSFIRE 3D HST (U V) rest frame quiescent star forming (V J) rest frame

20 Properties of quiescent galaxies 1.5 log R e (kpc) SDSS (z 0) LRIS (1 < z < 1.5) MOSFIRE (1.5 < z < 2.5) log σ e (km/s) log M / M O log R e (kpc)

21 Dynamical masses 12.0 SDSS (z 0) LRIS (1 < z < 1.5) log M / M O MOSFIRE (1.5 < z < 2.5) The M dyn - M relation is constant with redshift log M dyn / M O dark matter fraction initial mass function (IMF) galaxy structure

22 Evolution along the Mass Plane

23 Which questions can we answer? star-forming galaxy red nugget local elliptical How do compact quiescent galaxies grow in size? What is the physical process responsible for quenching? What are the properties of the progenitors of compact quiescent galaxies?

24 Evolution at fixed σ All quiescent galaxies Quiescent galaxies with σ~250 km/s log R e (kpc) 0.5 z 0 log R e (kpc) 0.5 R e M < z < < z < R e M log M / M O log M / M O The progenitors are significantly smaller physical size growth

25 R e [kpc] R e [kpc] z = 0 z = 1 z = 2 z = 3 z = 4 Hopkins et al Evolution fixed σ relation) Formation (Gas-Rich Merger) Similar Gas-Rich Merger (R e M 0.6 ) Dry Merger with Similar (Compact) Elliptical (R e M 1.0 ) Dry/Mixed Mergers with Gas-Poor Disks/Later-Forming (Less Compact) Ellipticals (R e M ) z = 0 Relation 1/2 1/ log ( M sph / M ) igure 25. Tracks followed by early-forming systems from Figure 24 in the ize stellar mass plane. Top: symbol shape denotes the z = 0stellarmass labeled), and color denotes redshift (from black at z = 0toredatz = 4, as abeled). Points show the median tracks as in Figure 24 for systems which first ormed at a given redshift (the beginning of each plotted track). Lines show the = 0sizemassrelation(solid),withslopeR e M 0.6, and the same divided y a factor of 2 (dashed) and 4 (dotted). Bottom: vectors illustrate motion in he plane owing to different types of mergers, for a system that will have a ass M M at z = 0 but first forms as a compact M M pheroid ( 1/4 the size of a typical similar-mass system at z = 0) at z 3 4 log R e (kpc) just two equal-mass dry mergers, one with a similarly compact elliptical, one with a later-forming, less compact elliptical; the latter merger builds a more extended envelope and therefore moves the system more rapidly toward agreement with the z = 0 At sufficiently large masses (especially for galaxies at the center of massive clusters), minor mergers will increasingly dominate the growth of the galaxy (see, e.g., Maller et al. 2006; Zheng et al. 2007; Masjedietal. 2007); these will have similar effects Quiescent to those described galaxies here, and with mayσ~250 even furtherkm/s increase the size at z = 0(especiallyifsmallmergingsystemsaredisrupted 1.5 as they merge; in this case they will not contribute much to the central structure of the galaxy, but will increasingly build up an extended envelope at large radii). More detailed modeling of the structure R of, e.g., M 1.6±0.3 BCGs and the most massive (M M ) 1.0 galaxies should account for both major and minor mergers in dense environments. The effective radius therefore rapidly grows, and by z = 0the system lies on (or even somewhat above) the median size mass relation for systems of the same z = 0 stellar mass. The velocity 0.5 dispersion grows slightly as mass is accumulated, but since most of this mass is contributed from dissipationless 2 Rcomponents e M to the extended envelope (recall that a merger of two identical spheroids will leave σ unchanged), it does Rnot e contribute M 0.0 much, and the z = 0galaxyhasapeak(central)velocity dispersion 400 km s 1,largebutonly30%largerthanits initial central velocity dispersion and completely consistent with those observed 10.5 in the 11.0 most massive 11.5galaxies today 12.0 (Bernardi et al. 2006). In detail, log in fact, M / Mthe O predicted descendants of early compact systems here have similar abundances, velocity dispersions, and remarkably similar predicted locations in, e.g., the z = 0size mass,fundamentalplane,andfaber Jackson relations to the sample in Bernardi et al. (2006), suggesting that many of those systems may be the products of this process. For the most part, then, these extreme systems are completely The size growth is consistent with being due to minor mergers This does not mean that mergers can explain the amount of growth see also Newman et al. 2012, Nipoti et al consistent in all the properties we can predict here (effective radius, mass, velocity dispersion, BH mass, and profile shape/

26 Beyond velocity dispersions strongly lensed quiescent galaxy at z = 2.6 stellar rotation curve using absorption lines! Newman, Belli, and Ellis 2015

27 Stellar populations LRIS spectrum public photometry posterior distributions ssfr M age tau A V Z We fit simultaneously photometric and spectroscopic data using the Bayesian code pyspecfit (Newman et al. 2014) Tau models and Bruzual and Charlot (2003) templates

28 Breaking the degeneracies old, dust-free dusty, star-forming A V spectrum + photometry only photometry Both old ages and dust extinction produce a red SED The absorption lines allow us to measure the age and break the degeneracy Z Unfortunately, we cannot accurately derive metallicities log age/yr

29 Stellar populations (U V) rest frame Gyr Gyr Gyr A V = Gyr Gyr Gyr Evolve backwards in time each galaxy according to its star formation history Reconstruct the evolution in number of quiescent galaxies observed number (V J) rest frame cosmic time

30 Application: size evolution Number evolution Size evolution log Φ(t) (Mpc 3 ) log R maj (kpc) at M O redshift observed (Muzzin et al. 2013) inferred from star formation histories observed (van der Wel et al. 2014) inferred from star formation histories population growth individual growth x2 growth log number of galaxies on the red sequence cosmic time (Gyr)

31 Size evolution: results A consistent picture for the size evolution of quiescent galaxies: z = 2 z = 0 Both physical growth and progenitor bias contribute to the size evolution

32 Application: quenching star-forming galaxy red nugget local elliptical How do compact quiescent galaxies grow in size? What is the physical process responsible for quenching? What are the properties of the progenitors of compact quiescent galaxies?

33 Stellar populations 1 < z < 1.6 Tight red sequence of quiescent galaxies (U-V) rest-frame The red sequence is a sequence in age (Whitaker et al. 2013) Intermediate population in the green valley (V-J) rest-frame

34 Stellar populations blue cloud green valley red sequence (post-starburst) red sequence (old)

35 Two quenching channels? Green Valley: slow quenching, dust, large sizes Post-Starburst: fast quenching, no dust, small sizes

36 Application: progenitors star-forming galaxy red nugget local elliptical How do compact quiescent galaxies grow in size? What is the physical process responsible for quenching? What are the properties of the progenitors of compact quiescent galaxies?

37 Application: progenitors our best spectrum: 31719, z=2.09 SFR We add a burst to the tau model to study the most recent star formation time

38 Application: progenitors mass fraction formed in the burst redshift Galaxy is observed 2 Gyr age of the burst (Gyr) Big Bang Most of the stellar mass ( M ) was formed at z > 3, in less than 2 Gyr Progenitors must have SFR > 200 M / yr Constraint on the progenitors of quiescent galaxies, and on the quenching timescale

39 Summary We are now in the era of absorption lines at high redshift. Two methods to connect galaxies with their progenitors: 1Velocity Dispersions 2Stellar populations New tools to address important aspects of massive galaxies: size evolution / quenching / progenitors