Abstract
We estimate the amount of negative feedback energy injected into the interstellar medium (ISM) of the host galaxy of 3C 273, a prototypical radio-loud quasar. We obtained 93, 233, and 343 ...GHz continuum images with the Atacama Large Millimeter/submillimeter Array (ALMA). After self-calibration and point-source subtraction, we reach an image dynamic range of ∼85,000 at 93 GHz, ∼39,000 at 233 GHz, and ∼2500 at 343 GHz. These are currently the highest image dynamic range obtained using ALMA. We detect spatially extended millimeter emission associated with the host galaxy, cospatial with the extended emission line region (EELR) observed in the optical. The millimeter spectral energy distribution and comparison with centimeter data show that the extended emission cannot be explained by dust thermal emission or synchrotron or thermal bremsstrahlung arising from massive star formation. We interpret the extended millimeter emission as thermal bremsstrahlung from gas directly ionized by the central source. The extended flux indicates that at least ∼7% of the bolometric flux of the nuclear source was used to ionize atomic hydrogen in the host galaxy. The ionized gas is estimated to be as massive as 10
10
–10
11
M
⊙
, but the molecular gas fraction with respect to the stellar mass is consistent with other ellipticals, suggesting that direct ionization ISM by the QSO may not be sufficient to suppress star formation, or we are witnessing a short timescale before negative feedback becomes observable. The discovery of a radio counterpart to EELRs provides a new pathway to studying the QSO–host ISM interaction.
We report the discovery of 28 quasars and 7 luminous galaxies at 5.7 ≤ z ≤ 7.0. This is the tenth in a series of papers from the Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs) project, ...which exploits the deep multiband imaging data produced by the Hyper Suprime-Cam (HSC) Subaru Strategic Program survey. The total number of spectroscopically identified objects in SHELLQs has now grown to 93 high-z quasars, 31 high-z luminous galaxies, 16 O iii emitters at z ∼ 0.8, and 65 Galactic cool dwarfs (low-mass stars and brown dwarfs). These objects were found over 900 deg2, surveyed by HSC between 2014 March and 2018 January. The full quasar sample includes 18 objects with very strong and narrow Ly emission, whose stacked spectrum is clearly different from that of other quasars or galaxies. While the stacked spectrum shows N v λ1240 emission and resembles that of lower-z narrow-line quasars, the small Ly width may suggest a significant contribution from the host galaxies. Thus, these objects may be composites of quasars and star-forming galaxies.
We report the discovery of 41 new high-z quasars and luminous galaxies that were spectroscopically identified at 5.7 ≤ z ≤ 6.9. This is the fourth in a series of papers from the Subaru High-z ...Exploration of Low-Luminosity Quasars (SHELLQs) project, based on the deep multi-band imaging data collected by the Hyper Suprime-Cam (HSC) Subaru Strategic Program survey. We selected the photometric candidates using a Bayesian probabilistic algorithm and then carried out follow-up spectroscopy with the Gran Telescopio Canarias and the Subaru Telescope. Combined with the sample presented in the previous papers, we have now spectroscopically identified 137 extremely red HSC sources over about 650 deg2, which includes 64 high-z quasars, 24 high-z luminous galaxies, 6 O iii emitters at z ∼ 0.8, and 43 Galactic cool dwarfs (low-mass stars and brown dwarfs). The new quasars span in luminosity range from M1450 ∼ −26 to −22 mag, and continue to populate luminosities a few magnitudes lower than have been probed by previous wide-field surveys. In a companion paper, we derive the quasar luminosity function at z ∼ 6 over an unprecedentedly wide range of M1450 ∼ −28 to −21 mag, exploiting the SHELLQs and other survey outcomes.
Abstract
We investigate the cold-gas properties of massive Virgo galaxies (>10
9
M
⊙
) at <3
R
200
(
R
200
is the radius where the mean interior density is 200 times the critical density) on the ...projected phase-space diagram with the largest archival data set to date to understand the environmental effects on galaxy evolution in the Virgo cluster. We find lower H
i
and H
2
mass fractions and higher star formation efficiencies (SFEs) from H
i
and H
2
in the Virgo galaxies than in the field galaxies for matched stellar masses; the Virgo galaxies generally follow the field relationships between the offset from the main sequence of the star-forming galaxies Δ(MS) and the gas fractions and SFEs, to the slight offset to lower gas fractions or higher SFEs compared to field galaxies at Δ(MS) < 0; lower gas fractions in galaxies with smaller clustocentric distance and velocity; and lower gas fractions in the galaxies in the W cloud, a substructure of the Virgo cluster. Our results suggest the cold-gas properties of some Virgo galaxies are affected by their environment at least at 3
R
200
maybe via strangulation and/or preprocesses, and H
i
and H
2
in some galaxies are removed by ram pressure at <1.5
R
200
. Our data cannot rule out the possibility of other processes such as strangulation and galaxy harassment accounting for gas reduction in some galaxies at <1.5
R
200
. Future dedicated observations of a mass-limited complete sample are required for definitive conclusions.
We report ∼2″ resolution Atacama Large Millimeter/submillimeter Array observations of the HCN (1-0), HCO+ (1-0), CO (1-0), CO (2-1), and CO (3-2) lines toward the nearby merging double-nucleus galaxy ...NGC 3256. We find that the high-density gas outflow traced in HCN (1-0) and HCO+ (1-0) emission is colocated with the diffuse molecular outflow emanating from the southern nucleus, where a low-luminosity active galactic nucleus (AGN) is believed to be the dominant source of the far-infrared luminosity. On the other hand, the same lines were undetected in the outflow region associated with the northern nucleus, whose primary heating source is likely related to starburst activity without obvious signs of an AGN. Both the HCO+ (1-0)/CO (1-0) line ratio (i.e., dense gas fraction) and the CO (3-2)/CO (1-0) line ratio are larger in the southern outflow (0.20 0.04 and 1.3 0.2, respectively) than in the southern nucleus (0.08 0.01 and 0.7 0.1, respectively). By investigating these line ratios for each velocity component in the southern outflow, we find that the dense gas fraction increases and the CO (3-2)/CO (1-0) line ratio decreases toward the largest velocity offset. This suggests the existence of a two-phase (diffuse and clumpy) outflow. One possible scenario to produce such a two-phase outflow is an interaction between the jet and the interstellar medium, which possibly triggers shocks and/or star formation associated with the outflow.
A galaxy-galaxy merger and the subsequent triggering of starburst activity are fundamental processes linked to the morphological transformation of galaxies and the evolution of star formation across ...the history of the universe. Both nuclear and disk-wide starbursts are assumed to occur during the merger process. However, quantifying both nuclear and disk-wide star formation activity is nontrivial because the nuclear starburst is dusty in the most active merging starburst galaxies. This paper presents a new approach to this problem: combining hydrogen recombination lines in optical, millimeter, and free-free emission. Using NGC 3256 as a case study, Hβ, H40 , and free-free emissions are investigated using the Multi Unit Spectroscopic Explorer at the Very Large Telescope of the European Southern Observatory (MUSE) and the Atacama Large Millimeter/submillimeter Array (ALMA). The Hβ image obtained by MUSE identifies star-forming regions outside the nuclear regions, suggesting a disk-wide starburst. In contrast, the H40 image obtained by ALMA identifies a nuclear starburst where optical lines are undetected due to dust extinction (AV ∼ 25). Combining both MUSE and ALMA observations, we conclude that the total star formation rate (SFR) is 49 2 M yr−1 and the contributions from nuclear and disk-wide starbursts are ∼34% and ∼66%, respectively. This suggests the dominance of disk-wide star formation in NGC 3256. In addition, pixel-by-pixel analyses for disk-wide star-forming regions suggest that shock gas tracers (e.g., CH3OH) are enhanced where gas depletion time (τgas = Mgas/SFR) is long. This possibly means that merger-induced shocks regulate disk-wide star formation activities.
Abstract
In this paper, we use high-quality rest-UV spectra of three radio galaxies at
z
∼ 3 observed with the FORS2 camera on the Very Large Telescope to measure the flux of several emission lines, ...including relatively faint ones, such as N
iv
λ
1486, O
iii
λ
1663, and Ne
iv
λ
2424. Additionally, we collect fluxes of faint rest-UV emission lines in 12
z
∼ 3 radio galaxies from the literature. Previously, physical and chemical properties of narrow-line regions (NLRs) in high-
z
active galactic nuclei (AGNs) have been investigated mostly by using only strong rest-UV emission lines (e.g., N
v
λ
1240, C
iv
λ
1549, He
ii
λ
1640, and C
iii
λ
1909). Such strong-line diagnostics are based on various assumptions due to the limitation in the number of available emission-line constraints. In this work, both physical and chemical properties of NLR clouds in each object are estimated by fitting detailed photoionization models to the measured emission-line fluxes. We confirm that the metallicity of NLRs in AGNs at
z
∼ 3 is solar or supersolar, without assumptions about the gas density and ionization parameter thanks to the constraints from the faint emission lines. This result suggests that high-
z
radio galaxies are already chemically mature at
z
∼ 3.
Abstract
We present the spectroscopic discovery of 69 quasars at 5.8 <
z
< 7.0, drawn from the Hyper Suprime-Cam (HSC) Subaru Strategic Program (SSP) imaging survey data. This is the 16th publication ...from the Subaru High-
z
Exploration of Low-Luminosity Quasars (SHELLQs) project, and it completes identification of all but the faintest candidates (i.e.,
i
-band dropouts with
z
AB
< 24 and
y
-band detections, and
z
-band dropouts with
y
AB
< 24) with Bayesian quasar probability
P
Q
B
>
0.1
in the HSC-SSP third public data release (PDR3). The sample reported here also includes three quasars with
P
Q
B
<
0.1
at
z
∼ 6.6, which we selected in an effort to completely cover the reddest point sources with simple color cuts. The number of high-
z
quasars discovered in SHELLQs has now grown to 162, including 23 type II quasar candidates. This paper also presents identification of seven galaxies at 5.6 <
z
< 6.7, an O
iii
emitter at
z
= 0.954, and 31 Galactic cool stars and brown dwarfs. High-
z
quasars and galaxies compose 75% and 16%, respectively, of all the spectroscopic SHELLQs objects that pass our latest selection algorithm with the PDR3 photometry. That is, a total of 91% of the objects lie at
z
> 5.6. This demonstrates that the algorithm has very high efficiency, even though we are probing an unprecedentedly low luminosity population down to
M
1450
∼ −21 mag.
We present physical properties of radio galaxies (RGs) with f1.4 GHz > 1 mJy discovered by Subaru Hyper Suprime-Cam (HSC) and Very Large Array Faint Images of the Radio Sky at Twenty-Centimeters ...(FIRST) survey. For 1056 FIRST RGs at 0 < z ≤ 1.7 with HSC counterparts in about 100 deg2, we compiled multi-wavelength data of optical, near-infrared (IR), mid-IR, far-IR, and radio (150 MHz). We derived their color excess (E(B − V)*), stellar mass, star formation rate (SFR), IR luminosity, the ratio of IR and radio luminosity (qIR), and radio spectral index ( radio) that are derived from the spectral energy distribution (SED) fitting with CIGALE. We also estimated Eddington ratio based on stellar mass and integration of the best-fit SEDs of active galactic nucleus (AGN) component. We found that E(B − V)*, SFR, and IR luminosity clearly depend on redshift while stellar mass, qIR, and radio do not significantly depend on redshift. Since optically faint (iAB ≥ 21.3) RGs that are newly discovered by our RG survey tend to be high redshift, they tend to not only have a large dust extinction and low stellar mass but also have high SFR and AGN luminosity, high IR luminosity, and high Eddington ratio compared with optically bright ones. The physical properties of a fraction of RGs in our sample seem to differ from a classical view of RGs with massive stellar mass, low SFR, and low Eddington ratio, demonstrating that our RG survey with HSC and FIRST provides us curious RGs among entire RG population.
Abstract
We report optical spectroscopic observations of four blue-excess dust-obscured galaxies (BluDOGs) identified by the Subaru Hyper Suprime-Cam. BluDOGs are a subclass of dust-obscured galaxies ...(DOGs; defined with the extremely red color (
i
− 22)
AB
≥ 7.0; Toba et al., showing a significant flux excess in the optical
g
and
r
bands over the power-law fits to the fluxes at the longer wavelengths. Noboriguchi et al. have suggested that BluDOGs may correspond to the blowing-out phase involved in a gas-rich major-merger scenario. However, the detailed properties of BluDOGs are not understood because of the lack of spectroscopic information. In this work, we carry out deep optical spectroscopic observations of four BluDOGs using Subaru/FOCAS and VLT/FORS2. The obtained spectra show broad emission lines with extremely large equivalent widths, and a blue wing in the C
iv
line profile. The redshifts are between 2.2 and 3.3. The averaged rest-frame equivalent widths of the C
iv
lines are 160 ± 33 Å, ∼7 times higher than the average of a typical type 1 quasar. The FWHMs of their velocity profiles are between 1990 and 4470 km s
−1
, and their asymmetric parameters are 0.05 and 0.25. Such strong C
iv
lines significantly affect the broadband magnitudes, which are partly the origin of the blue excess seen in the spectral energy distribution of BluDOGs. Their estimated supermassive black hole masses are 1.1 × 10
8
<
M
BH
/
M
⊙
<5.5 × 10
8
. The inferred Eddington ratios of the BluDOGs are higher than 1 (1.1 <
λ
Edd
< 3.8), suggesting that the BluDOGs are in a rapidly evolving phase of supermassive black holes.
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