We present a physical characterization of MM J100026.36+021527.9 (a.k.a. "Mambo-9"), a dusty star-forming galaxy (DSFG) at z = 5.850 0.001. This is the highest-redshift unlensed DSFG (and fourth most ...distant overall) found to date and is the first source identified in a new 2 mm blank-field map in the COSMOS field. Though identified in prior samples of DSFGs at 850 m to 1.2 mm with unknown redshift, the detection at 2 mm prompted further follow-up as it indicated a much higher probability that the source was likely to sit at z > 4. Deep observations from the Atacama Large Millimeter and submillimeter Array (ALMA) presented here confirm the redshift through the secure detection of 12CO(J = 6→5) and p-H2O (21,1 → 20,2). Mambo-9 is composed of a pair of galaxies separated by 6 kpc with corresponding star formation rates of 590 M yr−1 and 220 M yr−1, total molecular hydrogen gas mass of (1.7 0.4) × 1011M , dust mass of (1.3 0.3) × 109M , and stellar mass of ( ) × 109M . The total halo mass, (3.3 0.8) × 1012M , is predicted to exceed 1015M by z = 0. The system is undergoing a merger-driven starburst that will increase the stellar mass of the system tenfold in τdepl = 40−80 Myr, converting its large molecular gas reservoir (gas fraction of ) into stars. Mambo-9 evaded firm spectroscopic identification for a decade, following a pattern that has emerged for some of the highest-redshift DSFGs found. And yet, the systematic identification of unlensed DSFGs like Mambo-9 is key to measuring the global contribution of obscured star formation to the star formation rate density at z 4, the formation of the first massive galaxies, and the formation of interstellar dust at early times ( 1 Gyr).
Abstract
Submillimeter observations reveal the star formation activity obscured by dust in the young Universe. It still remains unclear how galaxies detected at submillimeter wavelengths are related ...to ultraviolet/optical-selected galaxies in terms of their observed quantities, physical properties, and evolutionary stages. Deep near- and mid-infrared observational data are crucial to characterize the stellar properties of galaxies detected with submillimeter emission. In this study, we make use of a galaxy catalog from the Spitzer Matching survey of the UltraVISTA ultra-deep Stripes. By crossmatching with a submillimeter source catalog constructed with archival data of the Atacama Large Millimeter/submillimeter Array (ALMA), we search for galaxies at
z
> 2 with a submillimeter detection in our galaxy catalog. We find that the ALMA-detected galaxies at
z
> 2 are systematically massive and have redder
K
s
–4.5 colors than the nondetected galaxies. The redder colors are consistent with the larger dust reddening values of the ALMA-detected galaxies obtained from spectral energy distribution (SED) fitting. We also find that the ALMA-detected galaxies tend to have brighter 4.5
μ
m magnitudes. This may suggest that they tend to have smaller mass-to-light ratios and thus to be younger than star-forming galaxies fainter at submillimeter wavelengths with similar stellar masses. We identify starburst galaxies with high specific star formation rates among both ALMA-detected and nondetected SMUVS sources. Irrespective of their brightness at submillimeter wavelengths, these populations have similar dust reddening values, which may suggest a variety of dust SED shapes among the starburst galaxies at
z
> 2.
Abstract
Until now, our knowledge of the extragalactic universe at mid-infrared (mid-IR) wavelengths (>5
μ
m) was limited to rare active galactic nuclei and the brightest normal galaxies up to
z
∼ 3. ...The advent of JWST with its Mid-Infrared Instrument (MIRI) will revolutionize the ability of the mid-IR regime as a key wavelength domain to probe the high-
z
universe. In this work we present a first study of JWST MIRI 7.7
μ
m sources selected with >3
σ
significance from the lensing cluster field SMACS J0723.3-7327. We model their spectral energy distribution (SED) fitting with 13 JWST and Hubble Space Telescope broad bands, in order to obtain photometric redshifts and derived physical parameters for all these sources. We find that this 7.7
μ
m galaxy sample is mainly composed of normal galaxies up to
z
= 4 and has a tail of about 2% of sources at higher redshifts to
z
≈ 9–10. The vast majority of our galaxies have 3.6–7.7 < 0 colors and very few of them need high dust extinction values (
A
V
= 3–6 mag) for their SED fitting. The resulting lensing-corrected stellar masses span the range 10
7
–10
11
M
⊙
. Overall, our results clearly show that the first MIRI 7.7
μ
m observations of deep fields are already useful to probe the high-redshift universe and suggest that the deeper 7.7
μ
m observations to be available very soon will open up, for the first time, the epoch of reionization at mid-IR wavelengths.
We present 16 new ultrabright HAB 25 galaxy candidates at z ∼ 8 identified over the COSMOS/UltraVISTA field. The new search takes advantage of the deepest-available ground-based optical and ...near-infrared observations, including the DR3 release of UltraVISTA and full-depth Spitzer/IRAC observations from the SMUVS and SPLASH programs. Candidates are selected using Lyman-break color criteria, combined with strict optical non-detection and SED-fitting criteria, designed to minimize contamination by low-redshift galaxies and low-mass stars. HST/WFC3 coverage from the DASH program reveals that one source evident in our ground-based near-IR data has significant substructure and may actually correspond to 3 separate z ∼ 8 objects, resulting in a total sample of 18 galaxies, 10 of which seem to be fairly robust (with a >97% probability of being at z > 7). The UV-continuum slope β for the bright z ∼ 8 sample is β = −2.2 0.6, bluer but still consistent with that of similarly bright galaxies at z ∼ 6 (β = −1.55 0.17) and z ∼ 7 (β = −1.75 0.18). Their typical stellar masses are M , with the SFRs of yr−1, specific SFR of Gyr−1, stellar ages of Myr, and low dust content mag. Using this sample we constrain the bright end of the z ∼ 8 UV luminosity function. When combined with recent empty field luminosity function estimates at similar redshifts, the resulting z ∼ 8 luminosity function can be equally well represented by either a Schechter or a double-power-law form. Assuming a Schechter parameterization, the best-fit characteristic magnitude is mag with a very steep faint-end slope . These new candidates include some of the brightest objects found at these redshifts, 0.5-1.0 magnitude brighter than those found over CANDELS, and providing excellent targets for spectroscopic and longer-wavelength follow-up studies.
Abstract
We present the characteristics of 2 mm selected sources from the largest Atacama Large Millimeter/submillimeter Array (ALMA) blank-field contiguous survey conducted to date, the Mapping ...Obscuration to Reionization with ALMA (MORA) survey covering 184 arcmin
2
at 2 mm. Twelve of 13 detections above 5
σ
are attributed to emission from galaxies, 11 of which are dominated by cold dust emission. These sources have a median redshift of
〈
z
2
mm
〉
=
3.6
−
0.3
+
0.4
primarily based on optical/near-infrared photometric redshifts with some spectroscopic redshifts, with 77% ± 11% of sources at
z
> 3 and 38% ± 12% of sources at
z
> 4. This implies that 2 mm selection is an efficient method for identifying the highest-redshift dusty star-forming galaxies (DSFGs). Lower-redshift DSFGs (
z
< 3) are far more numerous than those at
z
> 3 yet are likely to drop out at 2 mm. MORA shows that DSFGs with star formation rates in excess of 300
M
⊙
yr
−1
and a relative rarity of ∼10
−5
Mpc
−3
contribute ∼30% to the integrated star formation rate density at 3 <
z
< 6. The volume density of 2 mm selected DSFGs is consistent with predictions from some cosmological simulations and is similar to the volume density of their hypothesized descendants: massive, quiescent galaxies at
z
> 2. Analysis of MORA sources’ spectral energy distributions hint at steeper empirically measured dust emissivity indices than reported in typical literature studies, with
〈
β
〉
=
2.2
−
0.4
+
0.5
. The MORA survey represents an important step in taking census of obscured star formation in the universe’s first few billion years, but larger area 2 mm surveys are needed to more fully characterize this rare population and push to the detection of the universe’s first dusty galaxies.
Abstract
We study the relation between stellar mass (
M
*
) and star formation rate (SFR) for star-forming galaxies over approximately five decades in stellar mass (
5.5
≲
log
10
(
M
*
/
M
⊙
)
≲
10.5
...) at
z
≈ 3–6.5. This unprecedented coverage has been possible thanks to the joint analysis of blank non-lensed fields (COSMOS/SMUVS) and cluster lensing fields (Hubble Frontier Fields) that allow us to reach very low stellar masses. Previous works have revealed the existence of a clear bimodality in the
SFR–
M
*
plane with a star formation Main Sequence and a starburst cloud at
z
≈ 4–5. Here we show that this bimodality extends to all star-forming galaxies and is valid in the whole redshift range
z
≈ 3–6.5. We find that starbursts constitute at least ≈20% of all star-forming galaxies with
M
*
≳ 10
9
M
⊙
at these redshifts and reach a peak of 40% at
z
= 4–5. More importantly, 60%–90% of the total SFR budget at these redshifts is contained in starburst galaxies, indicating that the starburst mode of star formation is dominant at high redshifts. Almost all the low stellar mass starbursts with
log
10
(
M
*
/
M
⊙
)
≲
8.5
have ages comparable to the typical timescales of a starburst event, suggesting that these galaxies are being caught in the process of formation. Interestingly, galaxy formation models fail to predict the starburst/main-sequence bimodality and starbursts overall, suggesting that the starburst phenomenon may be driven by physical processes occurring at smaller scales than those probed by these models.
Abstract
We analyze a sample of 3300 galaxies between redshifts
z
≃ 3.5 and
z
≃ 8.5 selected from James Webb Space Telescope (JWST) images in the Hubble Ultra Deep Field and UKIDSS Ultra Deep Survey ...field, including objects with stellar masses as low as ≃10
8
M
⊙
up to
z
≃ 8. The depth and wavelength coverage of the JWST data allows us, for the first time, to derive robust stellar masses for such high-
z
, low stellar mass galaxies on an individual basis. We compute the galaxy stellar mass function, after complementing our sample with ancillary data from CANDELS to constrain the GMSF at high stellar masses (
M
>
M
*
). Our results show a steepening of the low stellar mass end slope (
α
) with redshift, with
α
= −1.61 ± 0.05 at
z
≃ 4 and
α
= −1.98 ± 0.14 at
z
≃ 7. We also observe an evolution of the normalization
ϕ
*
from
z
≃ 7 to
z
≃ 4, with
ϕ
z
≃
4
*
/
ϕ
z
≃
7
*
=
130
−
50
+
210
. Our study incorporates a novel method for the estimation of the Eddington bias, which takes into account its possible dependence both on stellar mass and redshift, while allowing for skewness in the error distribution. We finally compute the resulting cosmic stellar mass density and find a flatter evolution with redshift than previous studies.
Abstract
Recent controversy regarding the existence of massive (
log
(
M
*
/
M
⊙
)
≳
11
) galaxies at
z
> 6 poses a challenge for galaxy formation theories. Hence, it is of critical importance to ...understand the effects of SED fitting methods on stellar mass estimates of Epoch of Reionization galaxies. In this work, we perform a case study on the AGN host galaxy candidate COS-87259, with spectroscopic redshift
z
spec
= 6.853, that is claimed to have an extremely high stellar mass of
log
(
M
*
/
M
⊙
)
∼
11.2
. We test a suite of different SED fitting algorithms and stellar population models on our independently measured photometry in 17 broad bands for this source. Between five different code setups, the stellar mass estimates for COS-87259 span
log
(
M
*
/
M
⊙
)
=
10.24
–11.00, while the reduced
χ
2
values of the fits are all close to unity within
Δ
χ
ν
2
=
1.2
, such that the quality of the SED fits is basically indistinguishable. Only when we adopt a nonparametric star formation history model within
Prospector
do we retrieve a stellar mass exceeding
log
(
M
*
/
M
⊙
)
=
11
. Although the derived stellar masses change when using previously reported photometry for this source, the nonparametric SED-fitting method always yields the highest values. As these models are becoming increasingly popular for James Webb Space Telescope high-redshift science, we stress the absolute importance of testing various SED fitting routines particularly on apparently very massive galaxies at such high redshifts.
Abstract
Deep observations with the James Webb Space Telescope (JWST) have revealed an emerging population of red pointlike sources that could provide a link between the postulated supermassive black ...hole seeds and observed quasars. In this work, we present a JWST/NIRSpec spectrum from the JWST Cycle 1 UNCOVER Treasury survey of a massive accreting black hole at
z
= 8.50 displaying a clear broad-line component as inferred from the H
β
line with FWHM = 3439 ± 413 km s
−1
, typical of the broad-line region of an active galactic nucleus (AGN). The AGN nature of this object is further supported by high ionization, as inferred from emission lines, and a point-source morphology. We compute a black hole mass of
log
10
(
M
BH
/
M
⊙
)
=
8.17
±
0.42
and a bolometric luminosity of
L
bol
∼ 6.6 × 10
45
erg s
−1
. These values imply that our object is accreting at ∼40% of the Eddington limit. Detailed modeling of the spectral energy distribution in the optical and near-infrared, together with constraints from ALMA, indicate an upper limit on the stellar mass of
log
10
(
M
*
/
M
⊙
)
<
8.7
, which would lead to an unprecedented ratio of black hole to host mass of at least ∼30%. This is orders of magnitude higher compared to the local QSOs but consistent with recent AGN studies at high redshift with JWST. This finding suggests that a nonnegligible fraction of supermassive black holes either started out from massive seeds and/or grew at a super-Eddington rate at high redshift. Given the predicted number densities of high-
z
faint AGN, future NIRSpec observations of larger samples will allow us to further investigate galaxy–black hole coevolution in the early Universe.
This paper describes new deep 3.6 and 4.5 m imaging of three UltraVISTA near-infrared survey stripes within the COSMOS field. The observations were carried out with Spitzer's Infrared Array Camera ...(IRAC) for the Spitzer Matching Survey of the UltraVISTA Deep Stripes (SMUVS). In this work we present our data reduction techniques, and document the resulting mosaics, coverage maps, and catalogs in both IRAC passbands for the three easternmost UltraVISTA survey stripes, covering a combined area of about 0.66 deg2, of which 0.45 deg2 have at least 20 hr of integration time. SMUVS reaches point-source sensitivities of about 25.0 AB mag (0.13 Jy) at both 3.6 and 4.5 m, with a significance of 4 , accounting for both survey sensitivity and source confusion. To this limit the SMUVS catalogs contain a total of ∼350,000 sources, each of which is detected significantly in at least one IRAC band. Because of its uniform and high sensitivity, relatively large area coverage, and the wide array of ancillary data available in COSMOS, the SMUVS survey will be useful for a large number of cosmological investigations. We make all images and catalogs described herein publicly available via the Spitzer Science Center.
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