Deep infrared studies of massive high redshift galaxies
Labbé, I.
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Labbé, I. (2004, October 13). Deep infrared studies of massive high redshift galaxies.
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CHAPTER
THREE
L a rg e D isk -L ik e G a la x ies a t Hig h Red sh ift
ABSTRAC T
Using d eep near-infrared im aging of th e H u bble D eep F ield S ou th with IS AAC on th e Very La rg e Telesco p e we fi nd 6 large d isk -lik e galax ies at red sh ifts z = 1.4 − 3.0. T h e galax ies, selected in Ks (2.2µ m ), are regu lar
and su rp risingly large in th e near-infrared (rest-fram e op tical), with face-on eff ective rad ii re = 0.0065 − 0.009 or 5.0 − 7.5 h−17 0 k p c in a Λ CD M cosm ology,
com p arable to th e M ilk y Way. T h e su rface brigh tness p rofi les are consistent with an ex p onential law over 2 −3 eff ective rad ii. T h e WF P C2 m orp h ologies in H u b b le S p a ce Telesco p e im aging (rest-fram e UV ) are irregu lar and sh ow com p lex aggregates of star-form ing regions ∼ 200
(∼ 15 h−1
7 0 k p c) across,
sym m etrically d istribu ted arou nd th e Ks-band centers. T h e sp ectral energy
d istribu tions sh ow clear break s in th e rest-fram e op tical. T h e break s are strongest in th e central regions of th e galax ies, and can be id entifi ed as th e age-sensitive B alm er/ 4000 ˚A break . T h e m ost straigh tforward interp retation is th at th ese galax ies are large d isk galax ies; d eep N IR d ata are ind isp ens-able for th is classifi cation. T h e cand id ate d isk s constitu te 50% of galax ies with LV & 6 × 10
10
h−2
7 0 L¯at z = 1.4 − 3.0. T h is d iscovery was not ex p ected
on th e basis of p reviou sly stu d ied sam p les. In p articu lar, th e H u bble D eep F ield N orth is d efi cient in large galax ies with th e m orp h ologies and p rofi les we rep ort h ere.
Ivo L a b b ´e , G re g ory R u d n ick , M a rijn Fra n x , E m a n u e le D a d d i, Pie te r G . va n D ok k u m , N a ta sch a M . F¨orste r S ch re ib e r, K on ra d K u ijk e n , A la n M oorw ood , H a n s-Wa lte r R ix , H u u b R ¨ottg e rin g , Ig n a c io Tru jillo, A rje n va n d e We l, Pa u l va n
54 3 La rg e d isk -lik e g a la x ies a t h ig h red sh ift
1
In tr o d u c tio n
D
isk g alax ies are believed to u n d erg o a relatively sim p le fo rm atio n p ro c ess in which g as c o o ls an d c o n trac ts in d ark m atter halo s to fo rm ro tatio n ally su p p o rted d isk s with ex p o n en tial lig ht p ro fi les (F all & Efstathio u 19 8 0 ; M o , M ao , & W hite 19 9 8 ). A c ritic al test o f an y theo ry o f g alax y fo rm atio n is to rep ro d u c e the o bserved p ro p erties an d evo lu tio n o f g alax y d isk s.Previo u s o p tic al sp ec tro sc o p y an d HS T im ag in g have yield ed a wealth o f d ata o n d isk g alax ies at z . 1. (e.g ., Vo g t et al. 19 9 6 , 19 9 7 ; L illy et al. 19 9 8 ; B ard en et al. 20 0 3), altho u g h c o n trad ic to ry c laim s have been m ad e reg ard in g the im p lic atio n s fo r the siz e an d lu m in o sity evo lu tio n with red shift (see L illy et al. 19 9 8 ; M ao , M o , & W hite 19 9 8 ; B ard en et al. 20 0 3), an d the im p o rtan c e o f su rfac e brig htn ess selec tio n eff ec ts (see S im ard et al. 19 9 9 ; B o u wen s & S ilk 20 0 2).
It is still u n k n o wn what the sp ac e d en sity an d p ro p erties are o f d isk g alax ies at su bstan tially hig her red shift. M an y g alax ies at z ∼ 3 have been id en tifi ed u sin g the effi c ien t U -d ro p o u t techn iq u e (S teid el et al. 19 9 6 a,b). M o st o f these o bjec ts are c o m p ac t with rad ii ∼ 1 − 2 h−1
7 0 kpc, while som e are larg e an d irreg u lar (G iavalisco, S teidel, & M acchetto 19 9 6; L owen thal et al. 19 9 7). H owever, the U -drop selection req u ires hig h far-U V su rface brig htn ess du e to active, spatially com pact, an d u n obscu red star form ation . As a resu lt, larg e an d U V -fain t disk g alax ies m ay have been overlooked an d, addition ally, the m orpholog ies of L B G s cou ld ju st reveal the u n obscu red star-form in g reg ion s rather than the m ore evolved u n derlyin g popu lation which form s the disk.
T he m ost direct eviden ce for the ex isten ce of larg e disks at hig h redshift has com e from observation s in the N IR , which provide access to the rest-fram e optical. H ere the con tin u u m lig ht is m ore in dicative of the distribu tion of stellar m ass than in the U V an d n ebu lar lin es are accessible for kin em atic m easu rem en ts. van D okku m & S tan ford (2001) discu ss a K-selected g alax y at z = 1.34 with a rotation velocity of ∼ 29 0 km s−1. E rb et al. (2003) detect ∼ 15 0 km s−1 rotation at ∼ 6 h−1
7 0 kpc radii in the Hα em ission lin e of g alax ies at z ∼ 2.3 an d M oorwood et al. (2003) fi n d & 100 km s−1 rotation at ∼ 6 h−1
7 0 kpc from the cen ter of a g alax y at z= 3.2, seen in the N IR spectru m of the [O III]λ5 007 ˚A em ission lin e.
T he im ag in g data in these stu dies, however, are of lim ited depth an d resolu -tion , m akin g it diffi cu lt to determ in e m orpholog ical properties. In this L etter, we presen t an an alysis of the rest-fram e u ltraviolet-to-optical m orpholog ies an d spec-tral en erg y distribu tion s (S E D s) of 6 larg e can didate disk g alax ies at z ∼ 1.4 − 3 u sin g the deepest g rou n dbased N IR dataset cu rren tly available (L abb´e et al. 2003). T hrou g hou t, we adopt a fl at Λ-dom in ated cosm olog y (Ω M = 0.3, Λ = 0.7, H0 = 70 h7 0 km s−
1
3.2 O b se rv a tio n s 55
2
O b se rva tio n s
We obtained 102 hours of NIR Js, H, and Ksimaging in the HDF-S (2.05×2.05) un-der excellent seeing (FWHM≈0.0046), using ISAAC (Moorwood 1997) on the VLT. The observations were taken as part of the Faint InfraRed Extragalactic Survey (FIRES; Franx et al. 2000). We combined our data with existing deep optical HST/ WFPC2 imaging (version 2; Casertano et al. 2000), in the U300, B4 5 0, V6 06 and I8 14 bands, and we assembled a Ks-selected catalog of sources with SExtractor (Bertin & Arnouts 1996). Photometric redshifts and rest-frame luminosities were derived by fitting a linear combination of empirical galaxy spectra and stellar popu-lation models to the observed flux points (Rudnick et al. 2001, 2003a). The reduced images, photometric catalog, and redshifts are presented in Labb´e et al. (2003) and are all available on-line at the FIRES homepage1
. Furthermore, we obtained op-tical spectroscopy with FORS1 on the VLT for some of the sources (Rudnick et al. 2003b). Additional redshifts were obtained from Vanz ella et al. (2002). As dis-cussed in Rudnick et al. (2001, 2003a), our photometric redshifts yield good agree-ment with the spectroscopic redshifts, with rms |zsp ec − zp h o t|/(1 + zsp ec) ≈ 0.05 for zsp ec > 1.4.
Large disk galaxies in the HDF-South were identified by fitting exponential profiles convolved with the Point Spread Function (PSF) to the Ks-band images. Six objects at z > 1.4 have eff ective radii re > 3.6 h−170 kpc, three of which have spectroscopic redshifts. The mean redshift of the sample is 2.4. We will focus on these large galaxies in the remainder of the Letter. The structural properties of the full Ks-selected sample will be discussed in Trujillo et al. (2003).
3
R e st-fra m e O p tic a l ve rsu s U V M o rp h o lo g y
The large galaxies are shown in Figure 1. They have a regular morphology in the ISAAC Ks-band (2.2µ m ), which probes rest-frame optical wavelengths between 5400 and 9000 ˚A. In contrast, the WFPC2 V6 06 and I8 14-band morphologies, which map the unobscured star-forming regions at rest-frame UV wavelengths between 1500 and 3300 ˚A, are irregular with several knots up to ∼ 200(∼ 15 h−1
70 kpc) apart, symmetrically distributed around the Ks-band centers. In a few cases the observed optical light is spatially almost distinct from the NIR.
As a result of the structure in the WFPC2 imaging, 4 of the large objects have been split up into two sources by Casertano et al (2003). Fig. 1 shows the corresponding “ segmentation” map by “ SExtractor” which illustrates how the pixels in each image are allocated to diff erent sources. The galaxies were not split up when the Ks band image was used to detect objects. However, the broader PSF in the Ks-band image can play a role: if we smooth the I8 14-band data to the same resolution, we find that SExtractor only splits up 1 galaxy.
56 3 Larg e d isk -lik e g alax ies at h ig h red sh ift
Figure 1 —Le ft pa n e ls: The W FP C2 U300, averag ed V6 06 + I8 14 (rest-fram e U V ), and
o u r averag ed IS A A C H + Ksim ag es (rest-fram e o ptic al), sc aled pro po rtio nal to Fλwith
arbitrary no rm aliz atio n per g alax y . The rest-fram e U V m o rpho lo g ies are c o m plex and sy m m etric with respec t to the c enter o f the sm o o ther o ptic al d istribu tio n. M iddle pa n e ls: S E x trac to r’s I8 14-band seg m entatio n m ap, the sm o o thed I8 14 im ag es, and the Ks-band
im ag es after su btrac ting the sc aled , sm o o thed I8 14-band . Fro m the seg m entatio n m ap
it fo llo ws that d etec tio n in I8 14 wo u ld lik ely split u p m o st o f the so u rc es. The c entral
resid u als in Ks−Ism o o t h d em o nstrate that o ptic al and N IR lig ht are d istribu ted d iff erently
and that all g alax ies have a “ red ” nu c leu s. Rig h t pa n e ls: The rad ial pro fi les in the Ks
-band . The absc issa and the o rd inate are respec tively the m ean g eo m etric rad ial d istanc e and the su rfac e brig htness alo ng elliptic al iso pho tes. The arro ws m ark 1σ c o nfi d enc e intervals fo r m easu rem ents with sig nal-to -no ise less than 1. O verplo tted are the best-fi t ex po nential law (da sh ed), r1/4law (do tted), and po int+ex po nential (da sh -do t) fo r g alax y
4 9 4 and 6 11.
3.4 P rofi le fi ts and sizes 57
Ta b le 1 —Properties of hig h redshift disk g a la x ies in the H D F -S
Galaxya Kb
s,tot z MB,r estc µd0,B,r est ree,K r f 1/2,K r g 1/2,I ²h 302 19.70 1.439i -22.70 19.70 0.8 9 0.70 0.8 6 0.46 267 19.98 1.8 2 -22.8 8 19.92 0.75 0.74 0.8 8 0.37 257 20.25 2.027i -23.08 19.53 0.74 0.74 0.8 4 0.36 657 20.68 2.793i -23.56 19.33 0.76 0.70 0.74 0.18 611 20.53 2.94 -23.59 18 .51 0.65j 0.52 0.97 0.27 494 21.14 3.00 -23.31 18 .8 4 0.75j 0.56 0.8 6 0.47 aCatalog identification (L abb´e et al. 20 0 3 ) fK
s half-light radii (arcsec) bK
s-band total magnitudes gI814 half-ligt radii, matched to Ks
cRest-frame absolute B-band magnitudes hEllipticity
dFace-on rest-frame B-band surface brightnesses iSpectroscopic redshifts
eFace-on best-fit effective radii (arcsec) jTwo-component models
(point + exponential)
I814-band peaks might be expected in case of a chance superposition. Further-more, we performed photometric redshift analyses for subsections of the images and found no evidence for components at different redshifts.
4
P rofi le fi ts and siz es
Next, we fitted simple models convolved with the PSF (FWHM≈0.0046) to the two-dimensional surface brightness distributions in the Ks-band. The images are well-described by a simple exponential law over 2 − 3 effective radii (galaxy 302, 267, 257 and 657) or by a point source plus exponential (galaxy 611 and 494), where the point source presumably represents the light emitted by a compact bulge contributing about 40% of the light. We also derived intensity profiles by ellipse fitting. As can be seen in Figure 1, most galaxies are well described by an exponential. The central surface brightnesses and effective radii, enclosing half of the flux of the model profile, are corrected to face-on and shown in Table 1. The central surface brightness is multiplied with √1 − ², as an intermediate case between optically thin and optically thick, and corrected for cosmological dimming. The effective radii (semi-major axes) are surprisingly large, re = 0.0065 − 0.009 (5.0 − 7.5 h−1
70 kpc in a ΛCDM cosmology), comparable to the Milky Way and much larger than typical sizes of “normal” Ly-break galaxies (Giavalisco, Steidel, & Macchetto 1996; Lowenthal et al. 1997). As might be expected from the previous section, the I-band images have even larger effective radii. All galaxies have a “red” nucleus, and the colors become bluer in the outer parts.
ex-58 3 Large disk-like galaxies at high redshift
Figure 2 — The spectral energy distribution of source 611 in a 0.007 circular diameter
aperture (left) and in a concentric 100
− 200diameter ring (right), normalized to the Ks
-band fl ux. Overplotted are independent model fits from Rudnick et al. (2003a).
ponential disks and scattered, UV-bright star forming regions. Some even show evidence of well-developed grand-design spiral structure. However, the mean cen-tral surface brightness of the disks is 1 − 2 mag higher than that of nearby disk galaxies and the mean rest-frame color (U − V ) ≈ 0 is ∼ 1 mag bluer (c.f. Lilly et al. 1998). Passive evolution can lead to disks with normal surface brightnesses at low redshift. Alternatively, the disks are disrupted later by interactions or evolve into S0’s, which have higher surface brightnesses (e.g., Burstein 1979).
5
S pectral E nergy D istribution
The overall SEDs of the galaxies show a large variety. Four of the galaxies (257, 267, 494 and 657) satisfy conventional U-dropout criteria (Madau et al. 1996; Giavalisco & Dickinson 2001). One galaxy is at too low redshift (302) to be classified as a U-dropout, and one other galaxy is too faint in the rest-frame UV (611). It has Js− Ks > 2.3, and is part of the population of evolved galaxies identified by Franx et al (2003) and van Dokkum et al (2003).
3.6 D isc u ssion 59
6
Discussion
We have found 6 large galaxies with characteristics similar to those of nearby disk galaxies: exponential profiles with large scale lengths, more regular and centrally concentrated morphologies in the restframe optical than in the rest-frame UV, and, as a result, red nuclei. It is very tempting to classify these galaxies as disk galaxies, given the similarities with low redshift disk galaxies. However, kinematic studies are necessary to confirm that the material is in a rotating disk. Photometric studies of larger samples are needed to constrain the thickness of the disks. We note that simulations of Steinmetz & Navarro (2002) can show extended structures during a merging or accretion event. The expect duration of this phase is short, however, while the disk galaxies comprise a high fraction of the bright objects. It is therefore unlikely that a significant fraction of the galaxies presented here are undergoing such an event.
The density of these large disk galaxies is fairly low: over a survey area of 4.7 arcmin2
and to a magnitude limit of Ks,tot= 22 they make up 6 out of 52 galaxies at 1.4 . z . 3.0. However, they do constitute 6 out of the 12 most rest-frame luminous galaxies LV &6 × 1010h−270L¯in the same redshift range. The comoving volume density is ∼ 3 × 10−4 h3
70 Mpc−3 at a mean redshift z ≈ 2.3. Obviously, larger area surveys are needed to establish the true density. We note that three of the galaxies only have photometric redshifts, one of which (a U-drop galaxy at zpho t = 1.82) is in the poorly tested range 1.4 < z < 2.0. The volume density of disk galaxies with re > 3.6 h−170 kpc in the local universe is much higher at ∼ 3 × 10−3h3
70 Mpc
−3(de Jong 1996), although many nearby disks would not be present in our high redshift sample because their surface brightness would be too low.
We note that similar galaxies are absent in the very deep Near-IR imaging data on the HDF-N ( Williams et al. 1996; Dickinson 2000) Although notable differences between optical and NIR morphologies were reported for two of the largest LBGs in the HDF-N, no large galaxies were reported to have red nuclei and exponential profiles as in the HDF-S. The two fields are different in other aspects as well. We found earlier that the HDF-N is deficient in red sources (e.g., Labb´e et al. 2003 versus Papovich, Dickinson, & Ferguson 2001) and the disk galaxies are more luminous in the H-band than most of the high-redshift galaxies found in the HDF-N (Papovich, Dickinson, & Ferguson 2001). The larger number of red galaxies in the HDF-S (e.g., Labb´e et al. 2003, Franx et al. 2003) and their strong clustering (Daddi et al. 2003) may indicate that the red galaxies and large disks are both part of the same structures with high overdensities, and evolve into the highest overdensities at low redshift, i.e. clusters. If this is the case, the large disk galaxies may be the progenitor of large S0 galaxies in the nearby clusters, which have very similar colors as elliptical galaxies (e.g., Bower, Lucey, & Ellis 1992).
60 3 Large disk-like galaxies at high redshift is often assumed (Fall & Efstathiou 1980; Mo, Mao, & White 1998) that the disk scale length is determined by the spin parameter λ and the circular velocity of the virialized dark matter halo (Fall & Efstathiou 1980; Mo, Mao, & White 1998). For a ΛCDM cosmology, Mo, Mao, & White (1999) predict that the z ∼ 3 space density of large (re & 3.6 h−170 kpc) bright U-dropouts is 1.1×10
−4 h3
70 Mpc−3, whereas we find ∼ 2 × 10−4 h3
70 Mpc−3 for our 4 U-drops at a mean < z >∼ 2.4. This difference of a factor of two is not very significant, given our low number statistics and small survey volume. The combination of sizes and rotation velocities will give much stronger constraints on these models; it may be possible to measure the kinematics of some of these large galaxies using NIR spectrographs on large telescopes.
Ack now ledgments
We thank the staff at ESO for their hard work in taking these data and making them available. This research was supported by grants from the Netherlands Foundation for Research (NWO), the Leids K erkhoven-Bosscha Fonds, and the Lorentz Center. GR thanks Frank van den Bosch and Jarle Brinchmann for useful discussions.
References
Barden et al., 2003, ApJ , submitted (astro-ph/ 0302392) Bertin, E. & Arnouts, S. 1996, A&AS, 117, 393
Bouwens, R. & Silk, J . 2002, ApJ , 5 68 , 5 22
Bower, R. G ., Lucey, J . R., & Ellis, R. S. 1992, M NRAS, 25 4, 601 Burstein, D . 1979, ApJ , 234, 435
Casertano, S. et al., AJ , 120, pp. 2747– 28 24, 2000 D addi, E., et al., ApJ , in press
de J ong, R. S. 1996, A&A, 313, 45
D ickinson, M ., Philos. Trans. R. S oc . London A 358, p . 2 0 0 1 , 2 0 0 0 E rb e t a l., 2 0 0 3 , A p J , in p re ss
Fa ll, S . M . & E fsta thio u , G . 1 9 8 0 , M N R A S , 1 9 3 , 1 8 9 F¨o rste r S chre ib e r, N .M . e t a l. 2 0 0 3 , in p re p a ra tio n Fra n x , M . e t a l., The M essen g er 9 9 , p p . 2 0 – 2 2 , 2 0 0 0 Fra n x , M . e t a l. 2 0 0 3 , A p J , 5 8 7 , L 7 9
G ia va lisc o , M ., S te id e l, C . C ., & M a c che tto , F. D . 1 9 9 6 , A p J , 4 7 0 , 1 8 9 G ia va lisc o , M . & D ick in so n , M . 2 0 0 1 , A p J , 5 5 0 , 1 7 7
L a b b ´e , I. e t a l. 2 0 0 3 , A J , 1 2 5 , 1 1 0 7 L illy , S . e t a l. 1 9 9 8 , A p J , 5 0 0 , 7 5
L o we n tha l, J . D . e t a l. 1 9 9 7 , A p J , 4 8 1 , 6 7 3
M a d a u , P., Fe rg u so n , H . C ., D ick in so n , M . E ., G ia va lisc o , M ., S te id e l, C . C ., & Fru chte r, A ., M N R A S 2 8 3 , p p . 1 3 8 8 – 1 4 0 4 , 1 9 9 6
3.6 D isc u ssio n 61
Moorwood, A. F. 1997, Proc. SPIE, 2871, 1146
Moorwood, A., van Der Werf, P., Cuby, J.-G., O liva, E. 2003, Proceedings of the Work-shop on The Mass of Galaxies at Low and High Redshift, eds. R. B ender and A. Renz ini, Springer-Verlag, p302.
Steinm etz , M. & Navarro, J. F. 2002, New Astronom y, 7, 155 Papovich, C., Dickinson, M., & Ferguson, H. C. 2001, ApJ, 559, 620 Rudnick, G. et al. 2001, AJ, 122, 2205
Rudnick, G. et al. 2003a, in preparation Rudnick, G. et al. 2003b, in preparation
Schade, D., Lilly, S. J., Le Fevre, O ., Ham m er, F., & Cram pton, D. 1996, ApJ, 464, 79 Sim ard, L. et al. 1999, ApJ, 519, 563
Steidel, C. C., Giavalisco, M., Dickinson, M., & Adelberger, K . L. 1996, AJ, 112, 352 Steidel, C. C., Giavalisco, M., Pettini, M., Dickinson, M., & Adelberger, K . L. 1996, ApJ,
462, L17
Trujillo et al. 2003, in preparation
van Dokkum , P. G. & Stanford, S. A. 2001, ApJ, 562, L35 van Dokkum , P. G. et al. 2003, ApJ, 587, L83
Vanz ella, E. et al. 2002, A&A, 396, 847
Vogt, N. P., Forbes, D. A., Phillips, A. C., Gronwall, C., Faber, S. M., Illingworth, G. D., & K oo, D. C. 1996, ApJ, 465, L15
