SHARDS: Survey for High-z Absorption Red & Dead Sources

0.12 MB·English

by  Pablo G. Pérez-González

To appear in “Fourth Science with the GTC Meeting (2011)” RevMexAA(SC)
SHARDS: SURVEY FOR HIGH-Z ABSORPTION RED & DEAD SOURCES
Pablo G. P´erez-Gonza´lez,1,2 Antonio Cava,1 and the SHARDS Team3
RESUMEN
SHARDS (siglas en ingl´es de la Exploracio´n de galaxias con absorcio´n rojas y muertas a alto de-
splazamiento al rojo), un ESO/GTC Large Program, es una exploracio´n espectro-fotom´etrica super-profunda
2
(26.5 mag) realizada con GTC/OSIRIS y disen˜ada para seleccionar y estudiar galaxias masivas evolucionando
1
pasivamente a z=1.0–2.3 usando un juego de 24 filtros de anchura media (FWHM∼17 nm) a 500–950 nm
0
2 y apuntando a GOODS-N. Nuestra estrategia observacional ha sido ideada para detectar la marca espectral
conocidacomoabsorcio´ndeMg(a∼280nm),queconstituyeunacaracter´ısticadistintiva,necesariaysuficiente
n
a de las poblaciones estelares evoulcionadas(ma´s viejas que 0.5 Gyr). Nuestras observacionesesta´n siendo anal-
J izadas para: (1) construir por primera vez una muestra no sesgada de galaxias quiescentes a alto-z, llegando a

9 magnitudes m´as d´ebiles de lo conseguido hasta ahora con t´ecnicas espectrosco´picas y fotom´etricas;(2) derivar
edades y masas estelares precisas basa´ndonos en medidas robustas de ´ındices espectrales como el de Mg
UV
]
o D(4000); (3) estimar desplazamientos al rojo con una precisio´n de ∆z/(1+z)<0.02; y (4) estudiar galaxias
O
con l´ıneas de emisi´on (con formacio´n estelar o AGN) hasta desplazamientos al rojo altos. Adem´as, las SEDs
C
´opticas de resoluci´on intermedia proporcionadas por SHARDS ser´an de granutilidad para otras exploraciones
.
h cosmolo´gicas llevadas a cabo con otros telescopios (p.e., HST, Spitzer y Herschel).
p
- ABSTRACT
o
r SHARDS, an ESO/GTC Large Program, is an ultra-deep (26.5 mag) spectro-photometric survey with
t
s GTC/OSIRIS designed to select and study massive passively evolving galaxies at z=1.0–2.3 in the GOODS-
a N field using a set of 24 medium-band filters (FWHM∼17 nm) covering the 500–950 nm spectral range.
[
Our observing strategy has been planned to detect, for z>1 sources, the prominent Mg absorption feature

1 (at rest-frame ∼280 nm), a distinctive, necessary, and sufficient feature of evolved stellar populations (older
v
than 0.5 Gyr). These observations are being used to: (1) derive for the first time an unbiased sample of
0
high-z quiescent galaxies, which extends to fainter magnitudes the samples selected with color techniques and
0
8 spectroscopic surveys; (2) derive accurate ages and stellar masses based on robust measurements of spectral
1 features such as the Mg or D(4000) indices; (3) measure their redshift with an accuracy ∆z/(1+z)<0.02;
UV
1. and (4)study emission-line galaxies(starbursts andAGN) up to veryhigh redshifts. The well-sampledoptical
0 SEDs provided by SHARDS for all sources in the GOODS-N field are a valuable complement for current and
2 future surveys carried out with other telescopes (e.g., Spitzer, HST, and Herschel).
1
: Key Words: galaxies: photometry — galaxies: quiescent — galaxies: starburst — galaxies: high-redshift
v
i
X 1. INTRODUCTION et al. 2007) comparable to the density of a globu-
lar cluster (Buitrago et al. 2008). The existence of
r One of the most interesting results in Ex-
a very compact massive dead galaxiesat high-redshift
tragalactic Astronomy in the last decade is the dis-
is extremely challengingfor models of galaxyforma-
coveryofa numerouspopulationof massivegalaxies
tion,basedonthehierarchicalΛCDMparadigm(e.g,
(M∼>1011 M⊙) at high redshift (e.g., Franx et al.
Baugh et al. 1996, Cole et al. 2000, de Lucia et al.
2003). Some of them are already evolving passively
2006, Croton et al. 2006).
(Daddi et al. 2004), being good candidates for the
progenitors of massive nearby ellipticals (Hopkins
Inaddition, severalworkshavefoundcompelling
et al. 2009). Even more puzzlingly, these galaxies evidence of a high formation redshift (z∼>2) jointly
present very small sizes, and thus large mass den-
with a high star formation efficiency for the most
sities (Daddi et al. 2005, Trujillo et al. 2007, Toft
massive galaxies (Cimatti et al. 2006; Bundy et
al. 2007; P´erez-Gonza´lez et al. 2008a; Ilbert et al.
1Departamento de Astrof´ısica, Facultad de CC. F´ısicas,
2009), a scenario known as downsizing (Cowie et al.
UniversidadComplutensedeMadrid,E-28040Madrid,Spain
2AssociateAstronomeratStewardObservatory,UofA 1996). Furthermore, other studies report the detec-
3http://guaix.fis.ucm.es/∼pgperez/SHARDS/team.html tionofaredsequenceuptoz∼2,populatedbypost-
1
2 SHARDS TEAM
starburstgalaxies(Labb´e et al. 2007;Arnouts et al. SHARDS has completed 75% of the total 180
2007;Kriek etal. 2008;Fontanaet al. 2009). These hoursofobservingtimeawardedtotheproject,asof
works have shown that a key epoch for the study of January2012. Thedataqualityisexcellent,reaching
the formation of the red sequence is 1<z<2. fainterfluxesthanexpected(∼27mag)andvirtually
The SHARDS ESO/GTC Large Program aims all data present sub-arcsecondseeing.
at building an unbiased sample of quiescent ETGs
3. EMISSION-LINE GALAXIES IN SHARDS
at z>1 and providing with reliable observationales-
The comparison of fluxes measured in narrow-
timationsofrelevantquantitiessuchastheirnumber
bandimageswiththosefrombroad-banddatainthe
density,stellar masses,ages,andsizes. Reproducing
same spectral region is a widely used technique to
these results at high-z constitutes a major tests for
select and study galaxieswith emission-lines at low-
the predictions of galaxy formation models (de Lu-
andintermediate-(e.g.,Villaretal. 2008),andhigh-
cia et al. 2006, Croton et al. 2006, Hopkins et al.
redshifts (e.g., Ouchi et al. 2008). The technique is
2008). Therefore, our Large Program will be a sig-
basedonthedetectionofaprominentcolorwhenan
nificantstep forwardin our understanding of galaxy
emission-lineofagalaxy(atanappropriateredshift)
formation,sheddinglightintothe earlymassivestar
lieswithinthenarrow-bandfilterpass-band,incom-
formation events and quenching mechanisms.
parisonwithabroad-bandfilter,whosemeasurement
In this conference proceedings, we describe the
is dominated by the continuum around that line.
observationalstrategy of the survey and presentthe
first results obtained by SHARDS concerning the
study of emission-line galaxies at various redshifts,
and the characterization of red and dead sources at
z>1. Moreinformationaboutthe studyofemission-
line galaxies with SHARDS can be found in other
conference proceedings in this volume (Cava et al.
2012, Rodr´ıguez-Espinosaet al. 2012).
2. SURVEY DESCRIPTION
SHARDS is using OSIRIS on the Spanish 10.4m
telescope, GTC, to obtain medium-band imaging
through 24 filters (FWHM∼17 nm), and covering
the GOODS-N field down to the 26.5 mag (AB) in
each filter. Our goal is to probe the rest-frame UV
spectral range (250-350 nm) for galaxies at z>1.0,
counting with enough spectral resolution (R∼50) to
detect and accurately measure the Mg absorp-
UV
tion. This is a distinctive, necessary and sufficient
feature of massive quiescent ETGs at high redshift. Fig. 1. Redshift distribution of the galaxies selected
A positive detection of the feature with our spectro- as emission-line candidates using the SHARDS data at
photometric technique will confirm that the galax- 687nm. Thefilledhistogramreferstogalaxieswithcon-
ies are quiescent and provide us with an estimate firmed spec-z’s; the open histogram shows results based
of the age of the last star formation burst (Daddi onphoto-z’s(P´erez-Gonz´alezetal. 2008). Shadedbands
depicttheexpectedredshiftsforsourceswithemissionin
et al. 2005) and the galaxy redshift (with an ac-
typical lines (e.g., Hα, [OII], Lyα; some absorption fea-
curacy ∆z/(1+z)<0.02). OSIRIS provides imaging
tures are also shown) lying in the F687W17 filter.
capabilities up to λ∼950 nm, which means that we
can probe the Mg absorption at 1.0<z<2.3. In Cava et al. (2012), we demonstrate that
The resolution of this observing strategy is sim- SHARDS data can be used to segregate emission-
ilar to that used by the Grism ACS Program for line galaxies. That paper concentrates in the selec-
ExtragalacticScience (GRAPES;Daddietal. 2005) tion performed with the F687W17 SHARDS filter
and the Probing Evolution And Reionization Spec- (central wavelength: 687 nm; width: 17 nm). Here,
troscopically project (PEARS; PI: Malhotra) to inFigure1,wepresenttheredshifthistogramforthe
study quiescent ETGs through HST grism slitless emission-line galaxies selected in Cava et al. (2012).
spectroscopy. Ourprojectcovers10timesmorearea More than 75% of the spectroscopically confirmed
than the one used in Daddi et al. (who used the z∼0.8 [OII] emitters in the GOODS-N field are se-
UDF), and reach 1.5 mag fainter. lectedwithourmedium-banddata. Theresemblance
UPDATE ON SHARDS 3
Fig. 2. Postage stamps of aclose-pair of Lyman-αemit- Fig.3. SEDofJ123704.36+621335.0, oneofthespectro-
ters (LAEs) at z∼5 in the ultra-deep data taken in the scopically confirmed compact massive spheroidal galax-
GOODS-N field by Subaru (R-band, resolution R∼7) ies in GOODS-N (1011.03±0.04 M⊙, P´erez-Gonz´alez et
and GTC (SHARDSdata, R∼50). al. 2008; seealsoNewmanetal. 2010). Thebroad-band
data(blackandgraysymbols)havebeenfittedtoastel-
oftheredshiftdistributionbuiltwithphoto-z’s(open larpopulationmodel(inblue). SHARDSdata(depicted
histogram) with that built with spec-z’s (filled) is in orange jointly with filter widths and errors), and the
remarkable, and the density peaks are placed where positions of the Mg absorption feature (also formed by
one would expect a peak in the detection efficiency FeII lines) and the[OII] emission-line are marked.
based on the presence of an emission-line or absorp-
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