Galaxy SMM Research Articles

Kiloparsec-scale Imaging of the CO(1-0)-traced Cold Molecular Gas Reservoir in a z ∼ 3.4 Submillimeter Galaxy

We present a high-resolution study of the cold molecular gas as traced by CO(1-0) in the unlensed z ∼ 3.4 submillimeter galaxy SMM J13120+4242, using multiconfiguration observations with the Karl G. Jansky Very Large Array (JVLA). The gas reservoir, imaged on 0.″39 (∼3 kpc) scales, is resolved into two components separated by ∼11 kpc with a total extent of 16 ± 3 kpc. Despite the large spatial extent of the reservoir, the observations show a CO(1-0) FWHM linewidth of only 267 ± 64 km s−1. We derive a revised line luminosity of = (10 ± 3) × 1010 K km s−1 pc2 and a molecular gas mass of M gas = (13 ± 3)× 1010 (α CO/1) M ⊙. Despite the presence of a velocity gradient (consistent with previous resolved CO(6-5) imaging), the CO(1-0) imaging shows evidence for significant turbulent motions that are preventing the gas from fully settling into a disk. The system likely represents a merger in an advanced stage. Although the dynamical mass is highly uncertain, we use it to place an upper limit on the CO-to-H2 mass conversion factor α CO of 1.4. We revisit the SED fitting, finding that this galaxy lies on the very massive end of the main sequence at z = 3.4. Based on the low gas fraction, short gas depletion time, and evidence for a central AGN, we propose that SMM J13120 is in a rapid transitional phase between a merger-driven starburst and an unobscured quasar. The case of SMM J13120 highlights how mergers may drive important physical changes in galaxies without pushing them off the main sequence.

Milky Way–like Gas Excitation in an Ultrabright Submillimeter Galaxy at z = 1.6

Abstract Based on observations with the IRAM 30 m and Yebes 40 m telescopes, we report evidence of the detection of Milky Way–like, low-excitation molecular gas, up to the transition CO(J = 5–4), in a distant, dusty star-forming galaxy at z CO = 1.60454. WISE J122651.0+214958.8 (alias SDSS J1226, the Cosmic Seahorse), is strongly lensed by a foreground galaxy cluster at z = 0.44 with a source magnification of μ = 9.5 ± 0.7. This galaxy was selected by cross-correlating near-to-mid-infrared colors within the full-sky AllWISE survey, originally aiming to discover rare analogs of the archetypical strongly lensed submillimeter galaxy SMM J2135–0102, the Cosmic Eyelash. We derive an apparent (i.e., not corrected for lensing magnification) rest-frame 8–1000 μm infrared luminosity of μ L IR = 1.66 − 0.04 + 0.04 × 10 13 L ⊙ and apparent star formation rate μSFRIR = 2960 ± 70 M ⊙ yr−1. SDSS J1226 is ultrabright at S 350μm ≃ 170 mJy and shows similarly bright low-J CO line intensities as SMM J2135–0102, however, with exceptionally small CO(J = 5–4) intensity. We consider different scenarios to reconcile our observations with typical findings of high-z starbursts, and speculate about the presence of a previously unseen star formation mechanism in cosmic noon submillimeter galaxies. In conclusion, the remarkable low line luminosity ratio r 5,2 = 0.11 ± 0.02 is best explained by an extended, main-sequence star formation mode—representing a missing link between starbursts to low-luminosity systems during the epoch of peak star formation history.

Where infall meets outflows: turbulent dissipation probed by CH+ and Lyα in the starburst/AGN galaxy group SMM J02399−0136 at z ∼ 2.8

ABSTRACT We present a comparative analysis of the $\rm CH^+$(1–0) and Lyα lines, observed with the Atacama Large Millimeter Array and Keck telescope, respectively, in the field of the submillimetre-selected galaxy SMM J02399−0136 at z ∼ 2.8, which comprises a heavily obscured starburst galaxy and a broad absorption line quasar, immersed in a large Lyα nebula. This comparison highlights the critical role played by turbulence in channelling the energy across gas phases and scales, splitting the energy trail between hot/thermal and cool/turbulent phases in the circumgalactic medium (CGM). The unique chemical and spectroscopic properties of $\rm CH^+$ are used to infer the existence of a massive (∼3.5 × 1010 M⊙), highly turbulent reservoir of diffuse molecular gas of radius ∼20 kpc coinciding with the core of the Lyα nebula. The whole cool and cold CGM is shown to be inflowing towards the galaxies at a velocity ∼ 400 km s−1. Several kpc-scale shocks are detected tentatively in $\rm CH^+$ emission. Their linewidth and specific location in space and velocity with respect to the high-velocity Lyα emission suggest that they lie at the interface of the inflowing CGM and the high-velocity outflowing gas. They signpost the feeding of CGM turbulence by active galactic nuclei- and stellar-driven outflows. The mass and energy budgets of the CGM require net mass accretion at a rate commensurate with the star formation rate. From this similarity, we infer that the merger-driven burst of star formation and black-hole growth are ultimately fuelled by large-scale gas accretion.

The Discovery of a New Massive Molecular Gas Component Associated with the Submillimeter Galaxy SMM J02399-0136

Abstract We present CO(1–0), CO(3–2), and CO(7–6) observations using the Green Bank Telescope (GBT) and the Atacama Large Millimeter Array (ALMA) of the z = 2.8 submillimeter galaxy SMM J02399−0136. This was the first submillimeter-selected galaxy discovered and remains an archetype of the class, comprising a merger of several massive and active components, including a quasar-luminosity AGN and a highly obscured, gas-rich starburst spread over a ∼25 kpc extent. The GBT CO(1–0) line profile is comprised of two distinct velocity components separated by about 600 km s−1 and suggests the presence of a new component of molecular gas that had not been previously identified. The CO(3–2) observations with ALMA show that this new component, designated W1, is associated with a large extended structure stretching 13 kpc westward from the AGN. W1 is not detected in the ALMA CO(7–6) data, implying that this gas has much lower CO excitation than the central starburst regions, which are bright in CO(7–6). The molecular gas mass of W1 is about 30% of the total molecular gas mass in the system, depending on the CO-to-H2 conversion factor. W1 is arguably a merger remnant; alternatively, it could be a massive molecular outflow associated with the AGN, or perhaps inflowing metal-enriched molecular gas fueling the ongoing activity.

A near/mid infrared search for ultra-bright submillimetre galaxies: Searching for Cosmic Eyelash Analogues

We present results from a near/mid IR search for submillimetre galaxies over a region of 6230 sq deg. of the southern sky. We used a cross-correlation of the VISTA Hemispheric Survey (VHS) and the WISE database to identify bright galaxies (K_s <= 18.2) with near/mid IR colours similar to those of the high redshift lensed sub-mm galaxy SMM J2135-0102. We find 7 galaxies which fulfill all five adopted near/mid IR colour (NMIRQC) criteria and resemble the SED of the reference galaxy at these wavelengths. For these galaxies, which are broadly distributed in the sky, we determined photometric redshifts in the range z=1.6-3.2. We searched the VHS for clusters of galaxies, which may be acting as gravitational lenses, and found that 6 out of the 7 galaxies are located within 3.5 arcmin of a cluster/group of galaxies. Using the J-K_s vs J sequences we determine photometric redshifts for these clusters/groups in the range z=0.2-0.9. We propose the newly identified sources are ultra-bright high redshift lensed SMG candidates. Follow-up observations in the sub-mm and mm are key to determine the ultimate nature of these objects.

A MASSIVE MOLECULAR GAS RESERVOIR IN THE z = 2.221 TYPE-2 QUASAR HOST GALAXY SMM J0939+8315 LENSED BY THE RADIO GALAXY 3C220.3

ABSTRACT We report the detection of CO(J = 3 &rarr; ?> 2) line emission in the strongly lensed submillimeter galaxy (SMG) SMM J0939+8315 at z = 2.221, using the Combined Array for Research in Millimeter-wave Astronomy. SMM J0939+8315 hosts a type-2 quasar, and is gravitationally lensed by the radio galaxy 3C220.3 and its companion galaxy at z = 0.685. The 104 GHz continuum emission underlying the CO line is detected toward 3C220.3 with an integrated flux density of S cont = 7.4 ± 1.4 mJy. Using the CO(J = 3 &rarr; ?> 2) line intensity of I CO(3-2) = (12.6 ± 2.0) Jy km s−1, we derive a lensing- and excitation-corrected CO line luminosity of L CO(1-0) &prime; ?> = (3.4 ± 0.7) × 1010 (10.1/μ L) K km s−1 pc2 for the SMG, where μ L is the lensing magnification factor inferred from our lens modeling. This translates to a molecular gas mass of M gas = (2.7 ± 0.6) × 1010 (10.1/μ L) M ⊙. Fitting spectral energy distribution models to the (sub)-millimeter data of this SMG yields a dust temperature of T = 63.1 &minus; 1.3 &plus; 1.1 ?> K, a dust mass of M dust = (5.2 ± 2.1) × 108 (10.1/μ L) M ⊙, and a total infrared luminosity of L IR = (9.1 ± 1.2) ×1012 (10.1/μ L) L ⊙. We find that the properties of the interstellar medium of SMM J0939+8315 overlap with both SMGs and type-2 quasars. Hence, SMM J0939+8315 may be transitioning from a starbursting phase to an unobscured quasar phase as described by the “evolutionary link” model, according to which this system may represent an intermediate stage in the evolution of present-day galaxies at an earlier epoch.

EXCITATION CONDITIONS IN THE MULTI-COMPONENT SUBMILLIMETER GALAXY SMM J00266+1708

We present multiline CO observations of the complex submillimeter galaxy SMM J00266+1708. Using the Zpectrometer on the Green Bank Telescope, we provide the first precise spectroscopic measurement of its redshift (z=2.742). Based on followup CO(1-0), CO(3-2), and CO(5-4) mapping, SMM J00266+1708 appears to have two distinct components separated by ~500 km/s that are nearly coincident along our line of sight. The two components show hints of different kinematics, with the blue-shifted component dispersion-dominated and the red-shifted component showing a clear velocity gradient. CO line ratios differ slightly between the two components, indicating that the physical conditions in their molecular gas may not be alike. We tentatively infer that SMM J00266+1708 is an ongoing merger with a mass ratio of (7.8+/-4.0)/sin^2(i), with its overall size and surface brightness closely resembling that of other merging systems. We perform large velocity gradient modeling of the CO emission from both components and find that each component's properties are consistent with a single phase of molecular gas (i.e., a single temperatures and density); additional multi-phase modeling of the red-shifted component, although motivated by a CO(1-0) size larger than the CO(3-2) size, is inconclusive. SMM J00266+1708 provides evidence of early stage mergers within the submillimeter galaxy population. Continuum observations of J00266 at the ~1" resolution of our observations could not have distinguished between the two components due to their separation (0.73" +/- 0.06"), illustrating that the additional velocity information provided by spectral line studies is important for addressing the prevalence of unresolved galaxy pairs in low-resolution submillimeter surveys.

SMM J04135+10277: A CANDIDATE EARLY-STAGE “WET-DRY” MERGER OF TWO MASSIVE GALAXIES AT z = 2.8

We report interferometric imaging of CO(J=3-2) emission toward the z=2.846 submillimeter-selected galaxy SMM J04135+10277, using the Combined Array for Research in Millimeter-wave Astronomy (CARMA). SMM J04135+10277 was previously thought to be a gas-rich, submillimeter-selected quasar, with the highest molecular gas mass among high-z quasars reported in the literature. Our maps at ~6x improved linear resolution relative to earlier observations spatially resolve the emission on ~1.7" scales, corresponding to a (lensing-corrected) source radius of ~5.2 kpc. They also reveal that the molecular gas reservoir, and thus, likely the submillimeter emission, is not associated with the host galaxy of the quasar, but with an optically faint gas-rich galaxy at 5.2", or 41.5 kpc projected distance from the active galactic nucleus (AGN). The obscured gas-rich galaxy has a dynamical mass of M_dyn sin2(i)=5.6x10^11 M_sun, corresponding to a gas mass fraction of ~21%. Assuming a typical M_BH/M* ratio for z>2 quasars, the two galaxies in this system have an approximate mass ratio of ~1.9. Our findings suggest that this quasar-starburst galaxy pair could represent an early stage of a rare major, gas-rich/gas-poor ("wet-dry") merger of two massive galaxies at z=2.8, rather than a single, gas-rich AGN host galaxy. Such systems could play an important role in the early buildup of present-day massive galaxies through a submillimeter-luminous starburst phase, and may remain hidden in larger numbers among rest-frame far-infrared-selected quasar samples at low and high redshift.

VERY LARGE ARRAY MAPPING OF THE CO(1-0) LINE IN SMM J14011+0252

We present high-resolution CO(1-0) observations of the lensed submillimeter galaxy (SMG) SMM J14011+0252 at z=2.6. Comparison to the previously-detected CO(3-2) line gives an intensity ratio of r_3,1=0.97+/-0.16 in temperature units, larger than is typical for SMGs but within the range seen in the low-z ultraluminous infrared galaxy population. Combining our new data with previous mid-J CO observations, we perform a single-phase large velocity gradient (LVG) analysis to constrain the physical conditions of the molecular gas. Acceptable models have significant degeneracies between parameters, even when we rule out all models that produce optically thin emission, but we find that the bulk of the molecular gas has T_kin=20-60 K, n_{H_2}~10^4-10^5 cm^-3, and N_CO/Delta-v=10^{17.00+/-0.25} cm^-2 km^-1 s. For our best-fit models to self-consistently recover a typical CO-to-H_2 abundance and a plausible degree of virialization, the local velocity gradient in the molecular gas must be substantially larger than its galaxy-wide average. This conclusion is consistent with a scenario in which SMM J14011+0252 has a fairly face-on orientation and a molecular ISM composed of many unresolved clouds. Using previous H-alpha observations, we find that SMM J14011+0252 has a spatially resolved star formation rate vs. molecular gas surface density relation inconsistent with those of "normal" local star-forming galaxies, even if we adopt a local "disk-like" CO-to-H_2 conversion factor as motivated by our LVG analysis. This discrepancy supports the inference of a star formation relation for high-z starbursts distinct from the local relation that is not solely due to differing choices of gas mass conversion factor.

PROBING THE STAR FORMATION HISTORY AND INITIAL MASS FUNCTION OF THEz∼ 2.5 LENSED GALAXY SMM J163554.2+661225 WITHHERSCHEL

We present the analysis of Herschel SPIRE far-infrared (FIR) observations of the z = 2.515 lensed galaxy SMM J163554.2+661225. Combining new 250, 350, and 500 micron observations with existing data, we make an improved fit to the FIR spectral energy distribution (SED) of this galaxy. We find a total infrared (IR) luminosity of L(8--1000 micron) = 6.9 +/- 0.6x10^11 Lsol; a factor of 3 more precise over previous L_IR estimates for this galaxy, and one of the most accurate measurements for any galaxy at these redshifts. This FIR luminosity implies an unlensed star formation rate (SFR) for this galaxy of 119 +/- 10 Msol per yr, which is a factor of 1.9 +/- 0.35 lower than the SFR derived from the nebular Pa-alpha emission line (a 2.5-sigma discrepancy). Both SFR indicators assume identical Salpeter initial mass functions (IMF) with slope Gamma=2.35 over a mass range of 0.1 - 100 Msol, thus this discrepancy suggests that more ionizing photons may be necessary to account for the higher Pa-alpha-derived SFR. We examine a number of scenarios and find that the observations can be explained with a varying star formation history (SFH) due to an increasing star formation rate (SFR), paired with a slight flattening of the IMF. If the SFR is constant in time, then larger changes need to be made to the IMF by either increasing the upper-mass cutoff to ~ 200 Msol, or a flattening of the IMF slope to 1.9 +/- 0.15, or a combination of the two. These scenarios result in up to double the number of stars with masses above 20 Msol, which produce the requisite increase in ionizing photons over a Salpeter IMF with a constant SFH.

HERSCHEL-ATLAS GALAXY COUNTS AND HIGH-REDSHIFT LUMINOSITY FUNCTIONS: THE FORMATION OF MASSIVE EARLY-TYPE GALAXIES

Exploiting the Herschel-ATLAS Science Demonstration Phase (SDP) survey data, we have determined the luminosity functions (LFs) at rest-frame wavelengths of 100 and 250 micron and at several redshifts z>1, for bright sub-mm galaxies with star formation rates (SFR) >100 M_sun/yr. We find that the evolution of the comoving LF is strong up to z~2.5, and slows down at higher redshifts. From the LFs and the information on halo masses inferred from clustering analysis, we derived an average relation between SFR and halo mass (and its scatter). We also infer that the timescale of the main episode of dust-enshrouded star formation in massive halos (M_H>3*10^12 M_sun) amounts to ~7*10^8 yr. Given the SFRs, which are in the range 10^2-10^3 M_sun/yr, this timescale implies final stellar masses of order of 10^11-10^12 M_sun. The corresponding stellar mass function matches the observed mass function of passively evolving galaxies at z>1. The comparison of the statistics for sub-mm and UV selected galaxies suggests that the dust-free, UV bright phase, is >10^2 times shorter than the sub-mm bright phase, implying that the dust must form soon after the onset of star formation. Using a single reference Spectral Energy Distribution (SED; the one of the z~2.3 galaxy SMM J2135-0102), our simple physical model is able to reproduce not only the LFs at different redshifts > 1 but also the counts at wavelengths ranging from 250 micron to ~1 mm. Owing to the steepness of the counts and their relatively broad frequency range, this result suggests that the dispersion of sub-mm SEDs of z>1 galaxies around the reference one is rather small.

The properties of the interstellar medium within a star-forming galaxy at z= 2.3

We present an analysis of the molecular and atomic gas emission in the rest-frame far-infrared and sub-millimetre, from the lensed z=2.3 sub-millimetre galaxy SMM J2135-0102. We obtain very high signal-to-noise detections of 11 transitions from 3 species and limits on a further 20 transitions from 9 species. We use the 12CO, [CI] and HCN line strengths to investigate the gas mass, kinematic structure and interstellar medium (ISM) chemistry, and find strong evidence for a two-phase medium comprising a hot, dense, luminous component and an underlying extended cool, low-excitation massive component. Employing photo-dissociation region models we show that on average the molecular gas is exposed to a UV radiation field that is ~1000 x more intense than the Milky Way, with star-forming regions having a characteristic density of n~10^4 /cm^3. These conditions are similar to those found in local ULIRGs and in the central regions of typical starburst galaxies, even though the star formation rate is far higher in this system. The 12CO spectral line energy distribution and line profiles give strong evidence that the system comprises multiple kinematic components with different conditions, including temperature, and line ratios suggestive of high cosmic ray flux within clouds. We show that, when integrated over the galaxy, the gas and star-formation surface densities appear to follow the Kennicutt-Schmidt relation, although when compared to high-resolution sub-mm imaging, our data suggest that this relation breaks down on scales of <100pc. By virtue of the lens amplification, these observations uncover a wealth of information on the star formation and ISM at z~2.3 at a level of detail that has only recently become possible at z<0.1, and show the potential physical properties that will be studied in unlensed galaxies when ALMA is in full operation. (Abridged).

Gas, dust and stars in the SCUBA galaxy, SMM J0136: the EVLA reveals a colossal galactic nursery

We present new multiwavelength observations of the first submillimetre-selected galaxy (SMG) SMM J02399−0136 at z= 2.8. These observations include mapping of the CO J=1→0 emission using elements of the Expanded Very Large Array, as well as high-resolution 1.4-GHz imaging and optical/infrared (IR) data from the Very Large Array, Hubble Space Telescope, Spitzer and Keck-I. Together, these new data provide fundamental insights into the mass and distribution of stars, gas and dust within this archetypal SMG. The CO J=1→0 emission, with its minimal excitation and density requirements, traces the bulk of the metal-rich molecular gas, and reveals a molecular gas mass of ∼1011 M⊙, extending over approximately 5 arcsec (∼25 kpc in the source plane), although there is tentative evidence that it may be significantly larger. Our data suggest that three or more distinct structures are encompassed by this molecular gas reservoir, including the broad absorption line (BAL) quasar from which the redshift of the SMG was initially determined. In particular, the new rest-frame near-IR observations identify a massive, obscured, starburst which is coincident with a previously known Lyα cloud. This starburst dominates the far-IR emission from the system and requires a re-assessment of previous claims that the gas reservoir resides in a massive, extended disc around the BAL quasi-stellar object (QSO). Instead, it appears that SMM J02399−0136 comprises a merger between a far-IR-luminous, but highly obscured starburst, the BAL QSO host and a faint third component. Our findings suggest that this archetypal SMG and its immediate environment mark a vast and complex galactic nursery and that detailed studies of other SMGs are likely to uncover a similarly rich diversity of properties.

PASCHEN-α EMISSION IN THE GRAVITATIONALLY LENSED GALAXY SMM J163554.2+661225

We report the detection of the Paschen-alpha emission line in the z=2.515 galaxy SMM J163554.2+661225 using Spitzer spectroscopy. SMM J163554.2+661225 is a sub-millimeter-selected infrared (IR)-luminous galaxy maintaining a high star-formation rate (SFR), with no evidence of an AGN from optical or infrared spectroscopy, nor X-ray emission. This galaxy is lensed gravitationally by the cluster Abell 2218, making it accessible to Spitzer spectroscopy. Correcting for nebular extinction derived from the H-alpha and Pa-alpha lines, the dust-corrected luminosity is L(Pa-alpha) = (2.57+/-0.43) x 10^43 erg s^-1, which corresponds to an ionization rate, Q = (1.6+/-0.3) x 10^55 photons s^-1. The instantaneous SFR is 171+/-28 solar masses per year, assuming a Salpeter-like initial mass function. The total IR luminosity derived using 70, 450, and 850 micron data is L(IR) = (5-10) x 10^11 solar luminosities, corrected for gravitational lensing. This corresponds to a SFR=90-180 solar masses per year, where the upper range is consistent with that derived from the Paschen-alpha luminosity. While the L(8 micron) / L(Pa-alpha) ratio is consistent with the extrapolated relation observed in local galaxies and star-forming regions, the rest-frame 24 micron luminosity is significantly lower with respect to local galaxies of comparable Paschen-alpha luminosity. Thus, SMM J163554.2+661225 arguably lacks a warmer dust component (T ~ 70 K), which is associated with deeply embedded star formation, and which contrasts with local galaxies with comparable SFRs. Rather, the starburst is consistent with star-forming local galaxies with intrinsic luminosities, L(IR) ~ 10^10 solar luminosities, but "scaled-up" by a factor of 10-100.

Intense Star Formation and Feedback at High Redshift: Spatially Resolved Properties of thez= 2.6 Submillimeter Galaxy SMM J14011+0252

We present a detailed analysis of the spatially resolved properties of the lensed submillimeter galaxy (SMG) SMM J14011+0252 at z = 2.56, combining deep near-infrared integral-field data obtained with SPIFFI on the VLT with other multiwavelength data sets. As previously discussed by other authors, the broad characteristics of SMM J14011+0252 in particular and submillimeter galaxies in general are in agreement with what is expected for the early evolution of local massive spheroidal galaxies. From continuum and line flux, velocity, and dispersion maps, we measure the kinematics, star formation rates, gas densities, and extinction for individual subcomponents. The star formation intensity is similar to low-redshift while the line fluxes and the dynamics of the emission line gas provide direct evidence for a starburst-driven wind with physical properties very similar to local superwinds. We also find circumstantial evidence for self-regulated star formation within J1. The relative velocity of the bluer companion J2 yields a dynamical mass estimate for J1 within ~20 kpc of Mdyn ~ 1 × 1011 M☉. The relative metallicity of J2 is 0.4 dex lower than in J1n/J1s, suggesting different star formation histories. Spectral energy distribution fitting of the continuum peak J1c confirms and substantiates previous suggestions that this component is a z = 0.25 interloper. When removing J1c, the stellar continuum and Hα line emission appear well aligned spatially in two individual components, J1n and J1s, and coincide with two kinematically distinct regions in the velocity map, which might well indicate a merging system. This highlights the close similarity between SMGs and ultraluminous infrared galaxies (ULIRGs), which are often merger-driven maximal starbursts, and suggests that the intrinsic mechanisms of star formation and related feedback are in fact similar to low-redshift strongly star-forming systems.

HCN Observations of Submillimeter Galaxies and QSOs at High Redshift

We have conducted sensitive HCN(1-0) line observations of four high redshift submillimeter (sub-mm) galaxies and QSOs with the VLA. Although none is significantly detected in either line or continuum emission, thanks to the gravitational lens, sub-mm galaxy SMM J16359+6612 is marginally (at the 3-4σ level) detected once the three lensed components are stacked up. The HCN source appears to be double with a separation of ~1.5'', consistent with what has been implied from other observations. This first possible HCN detection of a submm galaxy, and three stringent HCN upper limits, combined with previous HCN detections and upper limits strongly constrain the HCN/CO ratios at high-z to be comparable to that of local ULIRGs.

New submillimeter diagnostics of physical properties of ISM in high redshift galaxies

AbstractWe present a new diagnosis method for determining physical properties of star-forming gas in high-z galaxies. In this method, we employed three key observational quantities, [CI], CO, and FIR luminosities, including our new detections of CO J = 4–3 emission from the pure-starburst (non-AGN) submm galaxy SMM J14011+0252 (z = 2.6) and the type-2 AGN IRAS FSC 10214+4724 (z = 2.3) obtained with the Nobeyama Millimeter Array (NMA) at the Nobeyama Radio Observatory. These two sources have extremely high star formation rate, and exhibit strong emission of CO and [CI] 609 μm lines. We determined ISM physical conditions for the two objects and another three high-z quasars in order to investigate the relationship between their ISM and power sources (i.e., massive star formation or AGN). A new PDR analysis (Wolfire et al. 2005, private communication) using CO, [CI], and FIR on five high-z sources provides new evidence that AGN host galaxies harbor denser (log nH ~ 5–6) ISM exposed to stronger far-UV fluxes of log G0 ~ 3.5–4 than the non-AGN submm galaxy. Volume filling factors of the star-forming dense gas in the AGN hosts are an order of magnitude smaller than that of the pure-starburst submm galaxy. This suggests that, in these AGN hosts, dense molecular clouds are dominating the central kpc around AGN, triggering extensive circumnuclear starbursts, and possibly feeding their central supermassive black hole simultaneously.

Nature of the Strongly Lensed Submillimeter Galaxy SMM J14011+0252

We have carried out near-infrared JHK spectroscopy of the gravitationally lensed submillimeter galaxy SMM J14011+0252 at z = 2.565, using the OH-airglow suppressor and the Cooled Infrared Camera and Spectrograph for OHS on the Subaru Telescope. This object consists of two optical components, J1 and J2, which are lensed by the cluster Abell 1835. J1 suffers additional strong lensing by a foreground galaxy at z = 0.25 in the cluster. The rest-frame optical Hα, Hβ, and [O II] λ3727 lines are detected in both J1 and J2, and [N II] λλ6548, 6583 lines are also detected in J1. A diagnosis of emission-line ratios shows that the excitation source of J1 is stellar in origin, consistent with previous X-ray observations. The continua of J1 and J2 show breaks at rest-frame 4000 A, indicating a relatively young age. Combined with optical photometry, we have carried out model-spectrum fitting of J2 and find that it is a very young (~50 Myr) galaxy of rather small mass (~108 M⊙) that suffers some amount of dust extinction. A new gravitational lensing model is constructed to assess both the magnification factor and contamination from the lensing galaxy of the component J1, using a Hubble Space Telescope F702W image. We have found that J1 suffers strong lensing with magnification of ~30, and its stellar mass is estimated to be 109 M⊙. These results suggest that SMM J14011+0252 is a major merger system at high redshift that undergoes intense star formation but is not a formation site of a giant elliptical galaxy. Still having plenty of gas, it will transform most of the gas into stars and will evolve into a galaxy of 1010 M⊙. Therefore, this system is possibly an ancestor of a present-day, less massive galaxy such as a midsized elliptical galaxy or a spiral galaxy.

Detection of CO from SMM J16359+6612, the Multiply Imaged Submillimeter Galaxy behind A2218

We report the detection of CO J = 3 → 2 line emission from all three multiple images (A, B, and C) of the intrinsically faint (0.8 mJy) submillimeter-selected galaxy SMM J16359+6612. The brightest source of the submillimeter continuum emission (B) also corresponds to the brightest CO emission, which is centered at z = 2.5168, consistent with the preexisting redshift derived from Hα. The observed CO flux in the A, B, and C images is 1.2, 3.5, and 1.6 Jy km s-1, respectively, with a line width of 500 ± 100 km s-1. After correcting for the lensing amplification, the CO flux corresponds to a molecular gas mass of ~2 × 1010 h M☉, while the extent of the CO emission indicates that the dynamical mass of the system is ~9 × 1010 M☉. Two velocity components are seen in the CO spectra; these could arise either from a rotating compact ring or disk of gas or from merging substructure. The star formation rate in this galaxy was previously derived to be ~100-500 M☉ yr-1. If all the CO emission arises from the inner few kiloparsecs of the galaxy and if the Galactic CO-to-H2 conversion factor holds, then the gas consumption timescale is a relatively short 40 Myr, and so the submillimeter emission from SMM J16359+6612 may be produced by a powerful but short-lived circumnuclear starburst event in an otherwise normal and representative high-redshift galaxy.

SPIFFI Observations of the Starburst SMM J14011+0252:Already Old, Fat, and Rich by z =2.565

Using the SPectrometer for Infrared Faint Field Imaging on the ESO Very Large Telescope, we have obtained J-, H-, and K-band integral field spectroscopy of the luminous submillimeter galaxy SMM J140110252. z p 2.565 A global spectrum reveals the brighter of this spatially resolved system’s two components as an intense starburst that is remarkably old, massive, and metal-rich for the early epoch at which it is observed. We see a strong Balmer break implying a ≥100 Myr timescale for continuous star formation as well as nebular emission-line ratios implying a supersolar oxygen abundance on large spatial scales. Overall, the system is rapidly converting a large baryonic mass into stars over the course of only a few hundred megayears. Our study thus adds new arguments to the growing evidence that submillimeter galaxies are more massive than Lyman break galaxies and more numerous at high redshift than predicted by current semianalytic models of galaxy evolution. Subject headings: galaxies: abundances — galaxies: evolution — galaxies: formation