62 research outputs found
Physical Properties, Star Formation, and Active Galactic Nucleus Activity in Balmer Break Galaxies at 0 < z < 1
We present a spectroscopic study with the derivation of the physical
properties of 37 Balmer break galaxies, which have the necessary lines to
locate them in star-forming-AGN diagnostic diagrams. These galaxies span a
redshift range from 0.045 to 0.93 and are somewhat less massive than similar
samples of previous works. The studied sample has multiwavelength photometric
data coverage from the ultraviolet to MIR Spitzer bands. We investigate the
connection between star formation and AGN activity via optical, mass-excitation
(MEx) and MIR diagnostic diagrams. Through optical diagrams, 31 (84%)
star-forming galaxies, 2 (5%) composite galaxies and 3 (8%) AGNs were
classified, whereas from the MEx diagram only one galaxy was classified as AGN.
A total of 19 galaxies have photometry available in all the IRAC/Spitzer bands.
Of these, 3 AGN candidates were not classified as AGN in the optical diagrams,
suggesting they are dusty/obscured AGNs, or that nuclear star formation has
diluted their contributions. Furthermore, the relationship between SFR surface
density (\Sigma_{SFR}) and stellar mass surface density per time unit
(\Sigma_{M_{\ast}/\tau}) as a function of redshift was investigated using the
[OII] \lambda3727, 3729, H\alpha \lambda6563 luminosities, which revealed that
both quantities are larger for higher redshift galaxies. We also studied the
SFR and SSFR versus stellar mass and color relations, with the more massive
galaxies having higher SFR values but lower SSFR values than less massive
galaxies. These results are consistent with previous ones showing that, at a
given mass, high-redshift galaxies have on average larger SFR and SSFR values
than low-redshift galaxies. Finally, bluer galaxies have larger SSFR values
than redder galaxies and for a given color the SSFR is larger for higher
redshift galaxies.Comment: preprint version, 36 pages, 17 figures, 3 tables, accepted for
publication in the Astrophysical Journa
J- and Ks-band Galaxy Counts and Color Distributions in the AKARI North Ecliptic Pole Field
We present the J- and Ks-band galaxy counts and galaxy colors covering 750
square arcminutes in the deep AKARI North Ecliptic Pole (NEP) field, using the
FLoridA Multi-object Imaging Near-ir Grism Observational Spectrometer
(FLAMINGOS) on the Kitt Peak National Observatory (KPNO) 2.1m telescope. The
limiting magnitudes with a signal-to-noise ratio of three in the deepest
regions are 21.85 and 20.15 in the J- and Ks-bands respectively in the Vega
magnitude system. The J- and Ks-band galaxy counts in the AKARI NEP field are
broadly in good agreement with those of other results in the literature,
however we find some indication of a change in the galaxy number count slope at
J~19.5 and over the magnitude range 18.0 < Ks < 19.5. We interpret this feature
as a change in the dominant population at these magnitudes because we also find
an associated change in the B - Ks color distribution at these magnitudes where
the number of blue samples in the magnitude range 18.5 < Ks < 19.5 is
significantly larger than that of Ks < 17.5
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AKARI observation of early-type galaxies in Abell 2218
We describe the AKARI InfraRed Camera (IRC) imaging observation of early-type galaxies (ETGs) in A2218 at z ≅ 0.175. With the imaging capability at 11 and 15 μm, we investigate mid-infrared (MIR) properties of ETGs in the cluster environment. Among our flux-limited sample of 22 optical red sequence ETGs, we find that more than 50% have MIR-excess emission, and the most likely cause of the MIR excess is the circumstellar dust emission from asymptotic giant branch (AGB) stars. The MIR-excess galaxies reveal a wide spread in N3-S11 (3 and 11 μm) colors, indicative of a significant spread (2–11 Gyr) in the mean ages of stellar populations. They are also preferentially located in the outer region, suggesting the environment dependence of MIR-excess ETGs over an area out to a half virial radius
Star Formation and AGN activity in Galaxies classified using the 1.6 {\mu}m Bump and PAH features at
We have studied the star-formation and AGN activity of massive galaxies in
the redshift range , which are detected in a deep survey field using
the AKARI InfraRed (IR) astronomical satellite and {\em Subaru} telescope
toward the North Ecliptic Pole (NEP). The AKARI/IRC Mid-InfraRed (MIR)
multiband photometry is used to trace their star-forming activities with the
Polycyclic-Aromatic Hydrocarbon (PAH) emissions, which is also used to
distinguish star-forming populations from AGN dominated ones and to estimate
the Star Formation Rate (SFR) derived from their total emitting IR (TIR)
luminosities. In combination with analyses of their stellar components, we have
studied the MIR SED features of star-forming and AGN-harboring galaxies.Comment: 45 pages and 63 figures, will be published in PASJ Vol.64 No.
Environmental dependence of 8 μm luminosity functions of galaxies at z ~ 0.8: Comparison between RXJ1716.4+6708 and the AKARI NEP-deep field
Aims. We aim to reveal environmental dependence of infrared luminosity functions (IR LFs) of galaxies at z ~ 0.8 using the AKARI
satellite. AKARI’s wide field of view and unique mid-IR filters help us to construct restframe 8 μm LFs directly without relying on
SED models.
Methods. We construct restframe 8 μm IR LFs in the cluster region RXJ1716.4+6708 at z = 0.81, and compare them with a blank
field using the AKARI north ecliptic pole deep field data at the same redshift. AKARI’s wide field of view (10' × 10') is suitable to
investigate wide range of galaxy environments. AKARI’s 15 μm filter is advantageous here since it directly probes restframe 8 μm at
z ~ 0.8, without relying on a large extrapolation based on a SED fit, which was the largest uncertainty in previous work.
Results. We have found that cluster IR LFs at restframe 8 μm have a factor of 2.4 smaller L^∗ and a steeper faint-end slope than that
of the field. Confirming this trend, we also found that faint-end slopes of the cluster LFs becomes flatter and flatter with decreasing
local galaxy density. These changes in LFs cannot be explained by a simple infall of field galaxy population into a cluster. Physics
that can preferentially suppress IR luminous galaxies in high density regions is required to explain the observed results
Multi-wavelength analysis of 18um-selected galaxies in the AKARI/IRC monitor field towards the North Ecliptic Pole
We present an initial analysis of AKARI 18um-selected galaxies using all 9
photometric bands at 2-24um available in the InfraRed Camera (IRC), in order to
demonstrate new capabilities of AKARI cosmological surveys. We detected 72
sources at 18um in an area of 50.2 arcmin^2 in the AKARI/IRC monitor field
towards the North Ecliptic Pole (NEP). From this sample, 25 galaxies with
probable redshifts z>~ 0.5 are selected with a single colour cut (N2-N3>0.1)
for a detailed SED analysis with ground-based BVRi'z'JK data. Using an SED
radiative transfer model of starbursts covering the wavelength range UV --
submm, we derive photometric redshifts from the optical-MIR SEDs of
18um-selected galaxies. From the best-fit SED models, we show that the IRC
all-band photometry is capable of tracing the steep rise in flux at the blue
side of the PAH 6.2um emission feature. This indicates that the IRC all-band
photometry is useful to constrain the redshift of infrared galaxies,
specifically for dusty galaxies with a less prominent 4000A break. Also, we
find that the flux dip between the PAH 7.7 and 11.2um emission feature is
recognizable in the observed SEDs of galaxies at z~1. By using such a colour
anomaly due to the PAH and silicate absorption features, unique samples of
ULIRGs at z~1, `silicate-break' galaxies, can be constructed from large
cosmological surveys of AKARI towards the NEP, i.e. the NEP-Deep and NEP-Wide
survey. This pilot study suggests the possibility of detecting many interesting
galaxy properties in the NEP-Deep and Wide surveys, such as a systematic
difference in SEDs between high- and low-z ULIRGs, and a large variation of the
PAH inter-band strength ratio in galaxies at high redshifts. [abridged]Comment: Accepted for publication in PASJ, AKARI special issu
Environmental dependence of 8um luminosity functions of galaxies at z~0.8: Comparison between RXJ1716.4+6708 and the AKARI NEP deep field
We aim to reveal environmental dependence of infrared luminosity functions
(IR LFs) of galaxies at z~0.8 using the AKARI satellite. We construct restframe
8um IR LFs in the cluster region RXJ1716.4+6708 at z=0.81, and compare them
with a blank field using the AKARI North Ecliptic Pole deep field data at the
same redshift. AKARI's wide field of view (10'x10') is suitable to investigate
wide range of galaxy environments. AKARI's 15um filter is advantageous here
since it directly probes restframe 8um at z~0.8, without relying on a large
extrapolation based on a SED fit, which was the largest uncertainty in previous
work. We have found that cluster IR LFs at restframe 8um have a factor of 2.4
smaller L^* and a steeper faint-end slope than that of the field. Confirming
this trend, we also found that faint-end slopes of the cluster LFs becomes
flatter and flatter with decreasing local galaxy density. These changes in LFs
cannot be explained by a simple infall of field galaxy population into a
cluster. Physics that can preferentially suppress IR luminous galaxies in high
density regions is required to explain the observed results.Comment: Accepted for publication in A&A AKARI special issu
Unveiling the Nature of Submillimeter Galaxy SXDF850.6
We present an 880 micron Submillimeter Array (SMA) detection of the
submillimeter galaxy SXDF850.6. SXDF850.6 is a bright source (S(850 micron) = 8
mJy) detected in the SCUBA Half Degree Extragalactic Survey (SHADES), and has
multiple possible radio counterparts in its deep radio image obtained at the
VLA. Our new SMA detection finds that the submm emission coincides with the
brightest radio emission that is found ~8" north of the coordinates determined
from SCUBA. Despite the lack of detectable counterparts in deep UV/optical
images, we find a source at the SMA position in near-infrared and longer
wavelength images. We perform SED model fits to UV-optical-IR photometry (u, B,
V, R, i', z', J, H, K, 3.6 micron, 4.5 micron, 5.8 micron, and 8.0 micron) and
to submm-radio photometry (850 micron, 880 micron, 1100 micron, and 21 cm)
independently, and we find both are well described by starburst templates at a
redshift of z ~= 2.2 (+/- 0.3). The best-fit parameters from the UV-optical-IR
SED fit are a redshift of z = 1.87 (+0.15/-0.07), a stellar mass of M_star =
2.5 +2.2/-0.3 x 10^11 M_sun, an extinction of A_V = 3.0 (+0.3/-1.0) mag, and an
age of 720 (+1880/-210) Myr. The submm-radio SED fit provides a consistent
redshift of z ~ 1.8-2.5, an IR luminosity of L_IR = (7-26) x 10^12 L_sun, and a
star formation rate of 1300-4500 M_sun/yr. These results suggest that SXDF850.6
is a mature system already having a massive amount of old stellar population
constructed before its submm bright phase and is experiencing a dusty
starburst, possibly induced by major mergers.Comment: 7 pages, 5 figures, Accepted for publication in Astrophysical Journa
Number Density Evolution of Ks -band Selected High Redshift Galaxy Populations in the AKARI North Ecliptic Pole Field
We present the number counts of Ks-band selected high redshift galaxy
populations such as extremely red objects (EROs), B, z & K -band selected
galaxies (BzKs) and distant red galaxies (DRGs) in the AKARI NEP field. The
final catalogue contains 308 EROs (Ks<19.0 ; 54 percent are dusty star-forming
EROs and the rest are passive old EROs), 137 star-forming BzKs and 38 passive
old BzKs (Ks<19.0) and 64 DRGs (Ks<18.6). We also produce individual component
source counts for both the dusty star-forming and passive populations. We
compare the observed number counts of the high redshift passively evolving
galaxy population with a backward pure luminosity evolution (PLE) model
allowing different degrees of number density evolution. We find that the PLE
model without density evolution fails to explain the observed counts at faint
magnitudes, while the model incorporating negative density evolution is
consistent with the observed counts of the passively evolving population. We
also compare our observed counts of dusty star-forming EROs with a
phenomenological evolutionary model postulating that the near-infrared EROs can
be explained by the source densities of the far-infrared - submillimetre
populations. Our model predicts that the dusty ERO source counts can be
explained assuming a 25 percent contribution of submillimetre star-forming
galaxies with the majority of brighter Ks -band detected dusty EROs having
luminous (rather than HR10 type ultra-luminous) submillimetre counterparts. We
propose that the fainter Ks>19.5 population is dominated by the sub-millijansky
submillimetre population. We also predict a turnover in in dusty ERO counts
around 19<Ks<20.Comment: (37 pages, 14 figures accepted for publication in The Astrophysical
Journal
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