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 Xu A. 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 ( astro-ph/ ) 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 (astro-ph/ ) The nature of (i-z) selected red objects in the UDF: stars, red and high redshift galaxies: Malhotra et al A z=5.45 lyman-alpha emitting galaxy with linear morphology in the GRAPES/UDF field: Rhoads et al Emission line objects and their redshifts in the UDF: Xu et al On high redshift massive ellipticals: Daddi et al Dwarfs and other stars in the UDF: Pirzkal et al HUDF morphologies of strong line emitters: Pirzkal et al AGNs in HUDF: Koekemoer et al 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~ 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

Need redder wavelengths for higher redshifts. We lose flux to IGM absorption below 1216 A rest-wavelength Sky brightness from the atmosphere becomes the limiting factor

Synergy with Ground Based Spectra Grapes will help ground based spectroscopy in at least two ways: “Instant” redshifts for ~ 300 to 500 objects; potential savings of time. Identification of which faint objects are worth a slitlet. Conversely, ground based data yield more flexible wavelength coverage and higher resolution, offering physical information unavailable with the grism.

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. possible 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].

40 orbits of UDF observations with the ACS grism Spectra for every source in the field. Good S/N continuum detections to I(AB) ~ 27 - about 2 magnitudes deeper than ground-based. about 15% of UDF sources ~ 1500 spectra. Spectral identification of every 4<z<7 object to I(AB)=27 Efficiently identifies spectroscopically interesting sources that might not merit a slit without the grism information: –high equivalent width lines; –Real z > 6 LBGs among the very red, faint stuff. Make reduced spectra public.

ACS Grism Characteristics (G800L + WFC) Dispersion: 40Å/pixel, Resolution: ~ 80Å (point source; scales with image size). Wavelength calibration is accurate ~10Å or  z~0.001 Wavelength coverage: ~ 550 nm to 1050 nm at “zero” response; 600 to 930 nm at half max.

The Epoch of Reionization The detection of Gunn-Peterson trough(s) in z ~ 6 quasars show the late stages of H reionization (Becker et al. 2001, Fan et al ) WMAP results indicate substantial reionization at z~15 Was the universe reionized twice (Cen 2002)?

Epoch of Galaxy formation? Early stages of galaxy formation are presumably ongoing at z~6. Spectroscopically confirmed samples at this redshift are small: less than a dozen galaxies at z>6, and four quasars at the very brightest end of luminosity function. We would like to determine the epoch and pace of reionization as well as the luminosity function of sources (galaxies/AGNs) responsible for the reionizing photons.

Testing Reionization with Lyman-α emitters 1.Low luminosity Lyman-α sources should not be visible before reionization: (Miralda-Escude 1998; Miralda-Escude & Rees 1998;Haiman & Spaans 1999; Loeb & Rybicki 1999) 2.These sources create local ionized bubbles allowing the Lyman-α photons to escape, esp. from the wings of the line (Lyman-α luminosity drops to 20-30% Haiman 2002, Santos 2003). Given the steep luminosity function we should be able to see this effect in a reasonable sample. 3.To distinguish this from evolution, use Lyman-break sample.

Ultradeep Field Grism Expectations: Lyman Break Galaxies No Lyman break galaxies have been identified from the ground at z > 5, except for the ones that have prominent lyman-alpha emission (….). Only 25% of LBGs show a lyman-alpha line at z=3 This seems to be purely a selection effect. It is very difficult to spectroscopically confirm a faint continuum break. 30A EW at z=6 implies 18 times the continuum flux in a few pixels. With GRAPES we can spectroscopically confirm LBGs to z= depending on the redshift.