High-redshift galaxies

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1 High-redshift galaxies Houjun Mo May 4, 2004 Galaxies can now be observed to z 6 Normal galaxies with 0.2 < z < 1 The Lyman-break population at z 3 The sub-mm sources at z 3 Between 1 2, spectroscopy desert, no strong optical lines

2 Galaxies at intermediate redshifts To redshifts z 1. Deep surveys in optical and near infrared. Photometric properties: evolutions in luminosity function, in galaxy sizes (or surface brightness) Evolution in morphological types: bulge/disk ratio, fraction of bar galaxies Kinematics: Rotation curves and velocity dispersions of galaxies; evolutions in the Tully-Fisher relation and in the fundamental-plane relations

3 The Lyman break galaxies The color selection technique:

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5 Redshift distribution

6 Luminosity function Observational band in R, λ 6800Å. At redshift 3, it corresponds to restframe wavelength 1700Å. UV luminosity may be used to estimate star formation rate: L UV = A SFR M yr 1ergs 1 Hz 1 where A = at 1500Å and A = at 2800Å for a Salpeter IMF; lower for a Scalo IMF.

7 Dust correction is the key Based on properties of local starburst galaxies. F(λ) λ β. β found linearly correlated with [ ] F(Hα)/F(Hβ) τ B ln 2.86 Power-law UV continuum: If no dust, then F(Hα)/F(Hβ) Calzetti et al. (1994) divided a sample of local star bursts according to τ B, using galaxies with the lowest τ B as unreddened template, and derived an effective extinction curve: Q n (λ) = τ n (λ)/(τ B,n τ B,1 ), τ n (λ) ln[f n (λ)/f 1 (λ)] 1 : unreddened template group; n : other group. Results: Q(x) = x 0.198x x 3 This can be used to get τ(λ)/τ B ; τ B can be measured or obtained from β.

8 Application to LBGs

9 Sizes distribution Typical size 1-2h 1 kpc, much smaller than the typical size of normal galaxies at z 0, 5h 1 kpc. Theoretical expectation: R H(z) 1 for a given circular velocity.

10 Kinematics and masses Based on spectral line profiles. Large velocity dispersion observed based interstellar absorption lines: kms 1. Deep potential wells? May be caused by non-gravitational motion. Nebular emission lines: associated with stars and so measure the motions of stars: kms 1. What does this mean for the halo mass of Lyman break galaxies?

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12 Clustering properties They are strongly correlated, correlation strength comparable to normal galaxies at z = 0. But it is expected in theory!

13 Connection to the local population of galaxies Based on size, total stars, velocity dispersion and clustering properties, LBGs are probably the progenitors of the bulges of spiral galaxies and and elliptical galaxies. But dust extinction makes it hard to infer the exact amount of stars in such a galaxy

14 Massive star-forming galaxies may be very dusty. Dust emission is in sub-mm band if galaxies at z 3. Thus, submm band is the way to go: SCUBA, MAMBO, SCUBA-II, HAWC- SOFIA, BOLOCAM-CSO, BOLOCAM- LMT, BLAST, SMA, ALMA, Extended VLA, SKA. Sub-mm sources

15 SED of starburst galaxies The inverse K-correction

16 Figure 1: SCUBA map

17 Idetifications and redshift measurements 2/3 of luminous SCUBA sources have radio counterparts, redshift measurements are possible. Some 60 galaxies Implied very large star formation rates: 1000M yr 1.

18 Clustering and masses Bright SCUBA sources are probably associated with massive halos. Together with their star formation rates, it is likely that they are the progenitors of massive ellipticals

19 Assuming bright SCUBA sources are associated in the most massive halos at z = 3 in ΛCDM model. Theoretical expectations

20 Star formation history t(z ): cosmic time z. ρ (z) = z ρ (z ) dt(z ) dz dz, ρ (z) = Ṁ dṁ P(Ṁ L,z)φ(L,z)dL = Ṁ (L,z)φ(L,z)dL, where P(Ṁ L,z)dṀ is the probability for a galaxy with luminosity L (in a given band) at redshift z to have star formation rate in the range (Ṁ,Ṁ + Ṁ ), and Ṁ (L,z) is the mean star formation rate Observations give φ(l,z)dl we need to know Ṁ (L,z)

21 Star formation diagnoses UV continuum: (Ṁ /M yr 1 ) (L UV /erg sec 1 Hz 1 ), where L UV is luminosity within Å Nebular Emission Lines: (Ṁ /M yr 1 ) (L Hα /erg sec 1 ) Forbidden Lines: (Ṁ /M yr 1 ) (L OII /erg sec 1 ), Far-infrared Continuum: (Ṁ /M yr 1 ) (L FIR /erg sec 1 ) for starbursts, where L FIR is the luminosity over the wavelength range µm.

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