Observations have revealed prodigious amounts of star formation in starburst galaxies as traced by dust and molecular emission, even at large redshifts. Recent work shows that for both nearby spiral galaxies and distant starbursts, the global star formation rate, as indicated by the infrared luminosity, has a tight and almost linear correlation with the amount of dense gas as traced by the luminosity of HCN. Our surveys of Galactic dense cores in HCN 1−0 emission show that this correlation continues to a much smaller scale, with nearly the same ratio of infrared luminosity to HCN luminosity found over 7-8 orders of magnitude in L IR , with a lower cutoff around 10 4.5 L ⊙ of infrared luminosity. The linear correlation suggests that we may understand distant star formation in terms of the known properties of local star-forming regions. Both the correlation and the luminosity cutoff can be explained if the basic unit of star formation in galaxies is a dense core, similar to those studied in our Galaxy.

We have mapped over 50 massive, dense clumps with four dense gas tracers: HCN J = 1 − 0 and 3 − 2; and CS J = 2 − 1 and 7 − 6 transitions. Spectral lines of optically thin H 13 CN 3-2 and C 34 S 5-4 were also obtained towards the map centers. These maps usually demonstrate single well-peaked distributions at our resolution, even with higher J transitions. The size, virial mass, surface density, and mean volume density within a well-defined angular size (FWHM) were calculated from the contour maps for each transition. We found that transitions with higher effective density usually trace the more compact, inner part of the clumps but have larger linewidths, leading to an inverse linewidth-size relation using different tracers. The mean surface densities are 0.29, 0.33, 0.78, 1.09 g cm −2 within FWHM contours of CS 2-1, HCN 1-0, HCN 3-2 and CS 7-6, respectively. We find no correlation of L IR with surface density and a possible inverse correlation with mean volume density, contrary to some theoretical expectations. Molecular line luminosities L ′ mol were derived for each transition. We see no evidence in the data for the relation between L ′ mol and mean density posited by modelers. The correlation between L ′ mol and the virial mass is roughly linear for each dense gas tracer. No obvious correlation was found between the line luminosity ratio and infrared luminosity, bolometric temperature, or the L IR /M V ir ratio. A nearly -2linear correlation was found between the infrared luminosity and the line luminosity of all dense gas tracers for these massive, dense clumps, with a lower cutoff in luminosity at L IR = 10 4.5 L ⊙ . The L IR -L ′ HCN 1−0 correlation agrees well with the one found in galaxies. These correlations indicate a constant star formation rate per unit mass from the scale of dense clumps to that of distant galaxies when the mass is measured for dense gas. These results support the suggestion that starburst galaxies may be understood as having a large fraction of gas in dense clumps.

Stern et al. (2012) presented a study of WISE selection of AGN in the 2 deg 2 COSMOS field, finding that a simple criterion W1-W2≥0.8 provides a highly reliable and complete AGN sample for W2<15.05, where the W1 and W2 passbands are centered at 3.4µm and 4.6µm, respectively. Here we extend this study using the larger 9 deg 2 NOAO Deep Wide-Field Survey Boötes field which also -2has considerably deeper WISE observations than the COSMOS field, and find that this simple color-cut significantly loses reliability at fainter fluxes. We define a modified selection criterion combining the W1−W2 color and the W2 magnitude to provide highly reliable or highly complete AGN samples for fainter WISE sources. In particular, we define a color-magnitude cut that finds 130±4 deg −2 AGN candidates for W2<17.11 with 90% reliability. Using the extensive UV through mid-IR broad-band photometry available in this field, we study the spectral energy distributions of WISE AGN candidates. We find that, as expected, the WISE AGN selection can identify highly obscured AGN, but that it is biased towards objects where the AGN dominates the bolometric luminosity output. We study the distribution of reddening in the AGN sample and discuss a formalism to account for sample incompleteness based on the step-wise maximum-likelihood method of Efstathiou et al. (1988). The resulting dust obscuration distributions depend strongly on AGN luminosity, consistent with the trend expected for a Simpson (2005) receding torus. At L AGN ∼ 3 × 10 44 erg s −1 , 29±7% of AGN are observed as Type 1, while at ∼ 4 × 10 45 erg s −1 the fraction is 64±13%. The distribution of obscuration values suggests that dust in the torus is present as both a diffuse medium and in optically thick clouds.

We have used the Caltech Submillimeter Observatory (CSO) to follow-up a sample of WISE-selected, hyperluminous galaxies, so called W1W2-dropout galaxies. This is a rare (∼ 1000 all-sky) population of galaxies at high redshift (peaks at z=2-3), that are faint or undetected by WISE at 3.4 and 4.6 µm, yet are clearly detected at 12 and 22 µm. The optical spectra of most of these galaxies show significant AGN activity. We observed 14 high-redshift (z > 1.7)W1W2-dropout galaxies with SHARC-II at 350 to 850 µm, with 9 detections; and observed 18 with Bolocam at 1.1 mm, with five detections. Warm Spitzer follow-up of 25 targets at 3.6 and 4.5 µm, as well as optical spectra of 12 targets are also presented in the paper. Combining WISE data with observations from warm Spitzer and CSO, we constructed their mid-IR to millimeter spectral energy distributions (SEDs). These SEDs have a consistent shape, showing significantly higher mid-IR to submm ratios than other galaxy templates, suggesting a hotter dust temperature. We estimate their dust temperatures to be 60 − 120 K using a single-temperature model. Their infrared luminosities are well over 10 13 L ⊙ . These SEDs are not well fitted with existing galaxy templates, suggesting they are a new population with very high luminosity and hot dust. They are likely among the most luminous galaxies in the Universe. We argue that they are extreme cases of luminous, hot dust-obscured galaxies (DOGs), possibly representing a short evolutionary phase during galaxy merging and evolution. A better understanding of their long-wavelength properties needs ALMA as well as Herschel data.

We present 20 Wide-field Infrared Survey Explorer (WISE)-selected galaxies with bolometric luminosities L bol > 10 14 L ☉ , including five with infrared luminosities L IR ≡ L (rest 8-1000 μm) > 10 14 L ☉ . These "extremely luminous infrared galaxies," or ELIRGs, were discovered using the "W1W2-dropout" selection criteria which requires marginal or non-detections at 3.4 and 4.6 μm (W1 and W2, respectively) but strong detections at 12 and 22 μm in the WISE survey. Their spectral energy distributions are dominated by emission at rest-frame 4-10 μm, suggesting that hot dust with T d ∼ 450 K is responsible for the high luminosities. These galaxies are likely powered by highly obscured active galactic nuclei (AGNs), and there is no evidence suggesting these systems are beamed or lensed. We compare this WISE-selected sample with 116 optically selected quasars that reach the same L bol level, corresponding to the most luminous unobscured quasars in the literature. We find that the rest-frame 5.8 and 7.8 μm luminosities of the WISE-selected ELIRGs can be 30%-80% higher than that of the unobscured quasars. The existence of AGNs with L bol > 10 14 L ☉ at z > 3 suggests that these supermassive black holes are born with large mass, or have very rapid mass assembly. For black hole seed masses ∼10 3 M ☉ , either sustained super-Eddington accretion is needed, or the radiative efficiency must be <15%, implying a black hole with slow spin, possibly due to chaotic accretion.

Observational evidence for inflowing motions in massive star forming regions has been extremely rare. We have made a spectroscopic survey of a sample of 28 massive star forming cores associated with water masers. An optically thick line of HCN (3-2) was used in combination with optically thin lines [H^{13}CN (3-2) or C^{34}S (5-4), (3-2), and (2-1)], to identify ``blue'' line profiles that can indicate inflow. Comparing intensities for 18 double-peaked line profiles yields 11 blue and 3 red profiles that are statistically significant. In the full sample of 28 sources, 12 show blue profiles and 6 show red profiles that are statistically significant based on the velocity offsets of lines that are optically thick from those that are optically thin. These results indicate that HCN (3-2) emission may trace inflow in regions forming high-mass stars.Comment: 6 pages, 2 figures. In press for Aug.1 ApJ Letter

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We report a new technique to select 1.6 < ∼ z < ∼ 4.6 dusty Lyman-alpha emitters (LAEs), over a third of which are 'blobs' (LABs) with emission extended on scales of 30-100 kpc. Combining data from the NASA Wide-field Infrared Survey Explorer (WISE) mission with optical spectroscopy from the W. M. Keck telescope, we present a color criteria that yields a 78% success rate in identifying rare, dusty LAEs of which at least 37% are LABs. The objects have a surface density of only ∼ 0.1 deg −2 , making them rare enough that they have been largely missed in narrow surveys. We measured spectroscopic redshifts for 92 of these WISE-selected, typically radio-quiet galaxies and find that the LAEs (LABs) have a median redshift of 2.3 (2.5). The WISE photometry coupled with data from Herschel a reveals that these galaxies have extreme far-infrared luminosities (L IR > ∼ 10 13−14 L ⊙ ) and warm colors, typically larger than submillimeter-selected galaxies (SMGs) and dust-obscured galaxies (DOGs). These traits are commonly associated with the dust being energized by intense AGN activity. We hypothesize that the combination of spatially extended Ly-α, large amounts of warm IR-luminous dust, and rarity (implying a short-lived phase) can be explained if the galaxies are undergoing strong 'feedback' transforming them from an extreme dusty starburst to a QSO.