infra luminous ultra-violet galaxies (i luv galaxies)

Infra Luminous Ultra-Violet galaxies(I LUV Galaxies)

Sangeeta Malhotra

(Space Telescope science Institute,

Arizona State University)

Need to go faint:

•GO back to redshift z > 6 and account for photons needed for reionization

•See ordinary galaxies, i.e. fainter than L*, because they make up most of the photons needed.

Need to go red:

Because of redshifting of the spectra and the IGM absorption.

Yan & Windhorst 2004

GRism ACS Program for Extragalactic Science (GRAPES)

Team: S. Malhotra, James Rhoads, Nor Pirzkal, Chun XuA. Cimatti, E. Daddi, H. Ferguson, J. Gardner, C. Gronwall, Z.

Haiman, A. Koekemoer, M. Kuemmel, L. Moustakas, A. Pasquali, N. Panagia, M. Stiavelli, S. di Serego Aligheri, Z.

Tsvetanov, J. Vernet, J. Walsh, R. Windhorst, H.J. Yan

Deepest Unbiased Spectroscopy yet. I(AB) < 27.5

To match the deepest imaging (Hubble Ultra Deep Field)

HST/ACS combination: 10 x fainter than ground

•Low sky background from space

•Contiguous redshift coverage,

•Red sensitivity of the ACS•High redshift galaxies are compact•Low resolution spectra - not all yield redshifts

1500 low res spectra, available from

www.stsci.edu/science/GRAPES

A Spiral galaxy at z=0.3

Direct image | Dispersed image

Experimental design (Pirzkal et al. 2004)

Four orients: large seperation of 90 degrees and small of 8 degrees: 0, 8, 90, 98 degrees orient. To disentangle overlapping spectra.

The agreement between the four orients in wavelength and flux demonstrate accurate flat-fielding and wavelength calibration.

Uses of spectroscopy

• Confirm redshifts - reliability of color selection at high Zs– (23/29 for (i-z)>0.9 and 14/15 for (i-z)>1.3)

• Completeness of color selection• Continuum slopes: stellar populations• Clustering

Morphology and spectrum of a young galaxy at z=5.42 +/- 0.7

• Rhoads et al. 2005.

Redshift confirmed with Keck (Stern et al., in prep), z=5.49 with no sign of AGN.

See poster by A. Verma for SEDs of this object with IRAC & MIPS.

High redshift galaxies

z=5.5, z=26.9

z=6.4, z=27.8

z=5.8, z=25.1

With GRAPES we can spectroscopically confirm LBGs to z’(AB)=27-28 depending on the redshift.

About 60 galaxies between z=4.5-6.7

Highest spectroscopic redshift in HUDF: z=6.7

stellar populations from the colors of the galaxies (Rhoads et al. 2005)

The composite spectrum of z~5 objects in the UDF : white line. The LBGs (Shapley et al.) at z=3: yellow. The bluest nearby galaxies NGC 1705 is in blue. More information about star-formation and gas with ALMA

A spike in the Redshift distribution

Comparison of observed redshift distribution (histogram) vs. expected numbers taking into account color selection, grism sensitivity and using Yan & Windhorst luminosity function.

The spike at z~6 is at least a factor of two overdense.

Deep probe vs. Flat-wide probe

• Ly-alpha emitters at z=5.7-5.77 observed with mosaic at CTIO

(36’x36’ = 88x88 cMpc)(Wang, Malhotra & Rhoads 2004)

• Inhomogeneous distribution– UDF is at the edge of it

Expected over-density

• HUDF was placed to include a known bright galaxy at z=5.83 (Dickinson et al. 2004) => overdensity of about 2 in the volume z=5.9+/-0.2

Need to “sharpen” the redshift distribution; probably a sharper peak

Would like to get the three dimensional structure.

Luminosity function at the overdensity

• Star-formation rate density for this over-dense region is 2-4x10-2

MO/Mpc3/year

• This is enough to drive re-ionization in this “local” over-density.

Spectroscopically identified objects:

from 600 to 6.7x1010 pc

Dead, red galaxies in a young universe

• More Ellipticals at z=1-2 than can be accounted for by hierarchical models of structure formation (Kauffamann \& Charlot 1998, Kauffmann et al. 1999). [Cimatti et al., McCarthy et al., Savaligo et al., Daddi et al.]

• More old ellipticals with no blue colors, i.e no recent star-formation (Sommerville et al. 2004) are seen at z~1-2 than semi-analytic models would produce.

• The problem is not that red galaxies are hard to produce; it is hard to produce red dead galaxies in such numbers (Nagamine et al. 2005).

Ellipticals at z=1.4-2.5 (Daddi et al. 2005)• 1011 solar masses and • ages of >1.5 Gyr. • Star-formation discontinued over

the last 0.5-1.5 Gyrs• Presence of AGNs in 2/7, support

the hypothesis that AGN feedback would “switch-off” star-formation (Granato et al. 2001, 2004, Springel et al. 2004).

• Space density about 2-3 times lower than at zero redshift (caveat: one small (3’x3’) ACS field)

Ellipticals at z~1 (Pasquali, Ferreras et al. 2005)

• • About 50% of the 18 galaxies at z~1 show dust lanes, blue disks in the center.

– This is similar to the fraction seen at z~0

• The ratio of disky/boxy ellipticals is about the same as local ellipticals

• We could passively evolve these galaxies to match the local population

Ellipticals at z~1 (Pasquali, Ferreras et al. 2005)

Old stellar populations (3 to 6 Gyrs) with metallicities ranging from 0.2 to 1.4 solar pointing to formation redshifts larger than 2

Emission line objects (Xu et al. 2005)

• Bulk of the redshifts come from emission line objects, i.e. star-forming galaxies between 0 < z < 1.5

• Estimate star-formation rates from these lines (Gronwall et al. 2005)

• Local peaks are seen in redshift space.

• Emission line objects seem interesting in other ways:

Size evolution of emission line selected objects:

• No discernable size evolution unlike that seen for continuum selected galaxies.

• Selection effect: easy to do spectroscopy of more compact galaxies. But these selection effects cannot account for the difference.

Pirzkal et al. 2005b

Properties of emission line galaxies: eGrapes

nearly all easily identified late type morphologies

Morphology appears to not be redshift dependent. Possible decrease in eGRAPES merger rate at z<1.0...eGRAPES have small (<2 kpc) -- no strong redshift dependenceeGRAPES have low masses (< 5 x 109 Mʘ)eGRAPES M/L decreases as a function of redshift...Older pop. at lower redshift, so peak of formation at z>1 ?68% of eGRAPES are LCBGs -- eGRAPES as extension of classic LCBGs?

Closest object in HUDF confirmed spectroscopically

• D=600 pc, M dwarf; red enough to be selected as a red (i-z’) > 0.9 source (Pirzkal et al. 2005).

• M-dwarfs to constrain the scale height of old disk: 400 +/ - 100 pc• White dwarfs to constrain the halo dark matter in WDs < 10%

Galactic structure (Pirzkal et al. 2005)

• M-dwarfs to constrain the scale height of old disk: 400 +/- 100 pc by comparing with models of Burgasser et al.

•Constrain the Galactic halo white dwarfs from proper motions.•If the age is 12 Gyr the constraints are white dwarfs < 10% of the Dark Matter halo of our Galaxy (Consistent with microlensing estimates)

Summary: too many, too few• Too few white dwarfs: < 10% of the DM halo (Pirzkal et al. 2005)• Ellipticals at z~1 much like z~0 (Pasquali et al. 2005)• Too many Ellipticals at z~2 (Daddi et al. 2005)• Large scale clustering at z~6 (Malhotra et al. 2005)

– Enough photons locally to reionize the intergalactic gas

• Line emitters do not follow halo growth in redshift (Pirzkal 2005)• Stellar populations at z~5, blue but normal (Rhoads et al. 2005)

Quantitative statements: need more than one field:

(Esp. in view of the large scale structure that we see)

8 more fields soon, at lower depth, to build up the statistics.

HST Treasury program in cycle 14: 200 orbits: PEARSPEARS