Star-formation and galaxy formation in the early universe.

Star-formation is put in by hand.

The case for wide-field spectroscopy from space:

•Need for wide-field•Need for space-based studies of high redshift •Feasibility of sensitive spectroscopy with the ACS grism

Sangeeta Malhotra, James Rhoads, Norbert Pirzkal, Chun Xu, Junxian Wang, Steve Dawson

The neighborhood of the Hubble Ultra Deep field

•One of the aims of the HUDF is to determine the galaxy population responsible for reionization at z~6.

Wang, Rhoads, Malhotra ‘04

•This image shows the wide-field distribution of lyman- emitters at z=5.8.

1/3 of a sq-degree at CTIO.

•HUDF lies on the edge of an overdensity at z~6.

• Ionizing photon budget at z~6 (e.g. Bunker et al. 2004)

Ouchi et al. z=4.86 Shimasaku et al. z=4.79

Palunas et al z=3.1

•Steidel et al at z=3.09.

•Campos et al. z=2.4

•Venemans et al. z=4.1

Advantages of HST/ACS combination:

• Contiguous wavelength/redshift coverage, unlike ground based instruments.

•Low sky background from space

•Red sensitivity of the ACS

•High redshift galaxies are compact, HST resolution helps

•Spatial resolution shows interesting structures that would be missed with ground based spectroscopy.

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, A. Pasquali, N. Panagia, L. Petro, M. Stiavelli, S. di Serego

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

Deepest Unbiased Spectroscopy yet. I(AB) < 27

To match the deepest imaging (Hubble Ultra Deep Field)

Science Goals• Probe reionization era by determining luminosity functions of

lyman- emitters, lyman-break galaxies at z=4-7 and low-luminosity AGNs.

• Study star-formation and galaxy assembly at 1<z<2 by identifying star-forming galaxies with strong emission lines and old populations with strong 4000Å break and any combination of the two.

• Cool dwarfs and halo white dwarfs.• Provide redshifts, thus enabling a wide variety of science and

better utilization of multiwavelength data: morphologies, x-ray properties, FIR properties …

• [your science here].

GRAPES Experimental Design

40 ACS/Grism orbits

Four orients: large separation of 90 degrees and small of 8 degrees: 0, 8, 90, 98 degrees orient to disentangle overlapping spectra

Excellent agreement between the four orients in wavelength and flux - accurate flat-fielding and wavelength calibration. z=0.1

Agreement with broadband flux requires sky subtraction to 10-4

A Spiral galaxy at z=0.3

Direct image | Dispersed image

Examples of spectra: Pirzkal et al. 2004 (astro-ph/0403458 )

Insert spectra from Nor’s paper here

Case of four (i-z) selected objects:

A quasar A lyman break galaxy

An ERO M sub-dwarf

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.

Morphology and spectrum of a young galaxy/AGN at z=5.45

Direct image | Dispersed image

Rhoads et al. 2004

Spectro-photometric redshifts at lower z• Can determine redshift where

two lines are detected.

• For one line sources we can use photometric redshifts to get fairly precise redshifts.

• In no line cases, we improve photometric redshifts by adding the grism data – like having 100 more filters.

• Comparison with photometric redshifts allow us to confirm and firm-up the redshifts. ( Xu, Mobasher et al. 2004).

• Robust M/L ratios through spectral fits (Pirzkal et al. 2004)

GRAPES papers• GRAPES, Grism Spectroscopy of the Hubble Ultra Deep Field:

Description and Data Reduction: Pirzkal et al. 2004 (astro-ph/0403458)• The nature of (i-z) selected red objects in the UDF: stars, red and high

redshift galaxies: Malhotra et al. 2004 • A z=5.45 lyman-alpha emitting galaxy with linear morphology in the

GRAPES/UDF field: Rhoads et al. 2004 • Emission line objects and their redshifts in the UDF: Xu et al. 2004 • On high redshift massive ellipticals: Daddi et al. 2004• Dwarfs and other stars in the UDF: Pirzkal et al. 2004 • HUDF morphologies of strong line emitters: Pirzkal et al. 2004• AGNs in HUDF: Koekemoer et al. 2004• The D4000-luminosity relation of morphologically-selected early type

galaxies at z~1 from the GRAPES: Moustakas et al. 2004

Science and Data Products

Science :

• Spectral identification of galaxies between 4<z<7, derive reliable luminosity function, ionizing photon budget etc. About 10 galaxies at z =6 and higher. Similar at =4-5.

• Galaxies with old stellar populations, HII region lines or both identified at z~0-1.6. About 200 spectral identifications in the UDF.

• M-dwarfs, white dwarfs (~30)

Reduced, extracted spectra to go in the public domain.

Wish list:• Think Wide-field

• Think grism

• Think IR 7 < z < 20