Download Y-band Imaging of Extragalatic Fields and High redshift

Y-band Imaging of Extragalatic Fields
and High redshift Quasars
Changsu Choi1, Myungshin Im1
1Center for the Exploration of the Origin of the Universe, Astronomy Program, Department of
Physics and Astronomy, Seoul National University
Abstract
We carried out the observations of several extragalactic fields, brown dwarfs, high-z QSO and A0V standard star imaging with Y-band filter at the Mt. Lemmon Opti
cal Astronomy Observatory (LOAO) and the Maidanak Observatory. The deepest limit magnitude of 260 minutes exposure is Y = 21.5 AB mag in case of LOAO and
Y = 22 AB mag for the Maidanak Observatory. Using the Y-band imaging data, we measured photometric calibration parameters of Y-band. We got two photometric
calibration parameters atmospheric extinction coefficient k = 0.087 and zero point ξ = 18.29 in LOAO , k = 0.1 and zero point ξ = 19.14 mag in Maidanak Obser
vatory. We performed number counts in Y-band imaging fields and found slopes consistent with previous I-band and J-band data. Also, we tested the usefulness of hig
h redshift QSO (z > 6) selection via i-z VS z-Y color-color diagram. The discrimination method between them with i-z va z-Y color-color diagram shows that it is as
effective as the i-Y vsY-J color-color diagram method which means we can search high redshift QSOs effectively with an optical CCD installed at 1m class telescopes
. Furthermore we analyzed characteristics of Y-band objects with color-magnitude diagram and redshift -Y-band magnitude relation.
Introduction
Results
Y-band is emerging as a key filter of recent
observations for its unique wavelength regi
on. But Past work with Y-band is still few an
d restricted stellar objects. It is good for id
entification of low mass stars and brown d
warf. (Hillenbrand et al. 2002)
 Extragalactic study with Y-band is very imp
ortant tool for high redshift objects. The m
ost highlighted aspect is High-z QSOs(z >6
) photometric selection method (Fan et al.
2000,2001; Warren & Hewett et al. 2002).
So Y-band is adopted to UKIDSS, Pan-STAR
RS on that purpose.
 We performed Deep Y-bang imaging of extr
agalactic fields with optical CCD at 1-m cla
ss telescope with these goals. 1.

Y-band transmission curve. Green line is z~7 QSO SED and
red line is L dwarf SED.
High-z QSO selection with color-color diagram
Venemans et al.(2007) high-z QSOs(black) is seperated
from dwarf stars(yellow)
•
1 mag deeper than UKIDSS (20.4 AB mag) and ah
ead of Pan-STARRS
•
2.Provide Photometric calibration data
•
3. Number count of detected sources for first time
in Y-band
•
4.Color-color diagram : high-z QSO selection met
hod
Here we present two results from our study.
1. Number count of our total observed field
2. Color-color Diagram of i-z vs z-Y

1.Number count

Bright end : stellar sources

Faint end : extended sources(extragalactic)

Number count shows intermediate feature
between I and J-band number count

Black circle is total objects and blue square
is stellar objects.
Data
.
Summary of observations
Log
(Exp.time
)
Area
(deg2)
Depth 5σ
(AB mag)
EGS
4.18
0.1
20.2
FLS
3.7
0.1
20.0
NEP
2.95~4.2
0.96
18.4~20.5
UKIDSS
3.4
0.1
19.2
# CFHT LS W1
3.75, 3.8
0.2
21.3
# NEP
3.9
0.2
21
#GRB090429B
4.0
0.1
21.8
*SDSS J113717+354956.9
3.4
0.1
19.2
*SDSS J084035+562419.9
3.7
0.1
19.8
*SDSS J084119+290504.4
3.65
0.1
19.7
*SDSS J092721+200123.7
3,7
0.1
19.6
*SDSS J125051+313021.9
3.7
0.1
19.6
SDSS J065405+652805.4
3.6
0.1
19.6
SDSS J083506+195304.3
3.5
0.1
19.1
SDSS J104335+121314.1
3.5
0.1
19.5
SDSS J121951+312849.4
3.5
0.1
19.0
SDSS J090900+652527.1
3.4
0.1
19.0
Target

We observed total 2 square deg using
LOAO 1m, Maidanak 1.5m telescope (#)

Observed targets are famous extragalactic
fields, 5 brown dwarf,(*) and 5 SDSS
QSOs (z~6). Details are on the table left.



We used IRAF tasks for Pre-process and
image stacking. SCAMP and SWARP is
used for astrometry. Reference catalog is
USNO B-1 catalog, its matching rms ~ 1”
A0V stars from HIPPARCOS catalog were
observed for standard star, which have zero
color. From that we calculated atmospheric
extinction coefficeint k = 0.05 ~ 0.1
We performed photometry using Source
Extractor and cross-matched with SDSS
DR7, CFHT LS T0003, UKIDSS DR2 plus,
CFHT-NEP matched catalog, DEEP2
redshift catalog

2. Color-Color Diagram i-z vs z-Y

Red line is SF galaxy evolution and
blue line represents QSOs as z goes
higher

In this figure, we can verify that i-z
vs z-Y color is effective method for
high –z QSO(stars) distinction from
L,T dwarfs(squares).

Black dot are observed Y-band
source. But we could not find high-z
QSO candidate from our
observation.
Discussion & Future works

We archived depth of 21mag with 2hr
exposure with 1-m class telescopes. It shows
potential of 1-m class telescopes with unique
and elaborated effort.

In right figure, Sensitivity limit of LOAO
versus Maidanak is shown. The difference is
about 1mag. Red arrow indicates 1mag
improved depth with refined mirror. Green
arrow indicate z-band depth of 60min
exposure.

Other application of Y-band imaging is GRB
afterglow observation. We carried out deep
Y-band imaging observation at LOAO &
Maidanak .

We try to search high-z QSOs with this
method with wider and deeper observations.
Summary

We observed 2 sq deg extragalactic fields, 5 QSOs and 5 dwarfs with Y-band filter.

We performed Y-band source number count and inspect Y-band sources.

We found i-z VS z-Y color-color diagram is effective method of high-z QSO photometric selection.

There are another potentialities of 1m class telescope and Y-band observation.

We try to search high-z QSOs(z>6) with this method and related works is undergoing.
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