Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Abstract: We present S82-20, an unusual redshift $\approx$3 object identified in SDSS-Stripe 82 broad-band images. The rest-frame ultraviolet spectrum of S82-20 shows emission lines from highly ionized species, including HeII $\lambda$1640, and the CIV $\lambda\lambda$1548, 1550 and OVI $\lambda\lambda$1032, 1038 doublets. The high Ly$\alpha$ luminosity ($3.5\times 10^{44}$ erg s$^{-1}$), the high emission line equivalent widths ($>200$\r{A} for Ly$\alpha$), the FWHM of the emission lines ($<800$km s$^{-1}$), and the high ionization OVI line strongly support the interpretation that S82-20 is a Type~II QSO. However, photoionization models using Type~II QSO do not fully explain the measured CIV/HeII line ratio, which requires either some contribution from star-formation or high velocity shocks. Additionally, S82-20 is not detected at wavelengths longer than 2$\mu$m, in tension with the expectation of isotropically IR emission of a luminous QSO. We consider the possibility that S82-20 is a rare example of a changing-look QSO, observed in a temporarily low state, where the broad line region has faded, while the narrow line region still emits emission line. Otherwise, it may be a rare case of the short phase of the life of a massive galaxy, in which active star formation and accretion onto a supermassive black hole coexist.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Abstract: ALMA observations of the long wavelength dust continuum are used to estimate the gas masses in a sample of 708 star-forming (SF) galaxies at z = 0.3 to 4.5. We determine the dependence of gas masses and star formation efficiencies (SFE=SFR per unit gass mass). We find that 70 percent of the increase in SFRs of the MS is due to the increased gas masses at earlier epochs while 30 percent is due to increased efficiency of SF. For galaxies above the MS this is reversed with 70 percent of the increased SFR relative to the MS being due to elevated SFEs. Thus, the major evolution of star formation activity at early epochs is driven by increased gas masses, while the starburst activity taking galaxies above the MS is due to enhanced triggering of star formation (likely due to galactic merging). The interstellar gas peaks at z = 2 and dominates the stellar mass down to z = 1.2. Accretion rates needed to maintain continuity of the MS evolution exceed 100 Msun per yr at z > 2. The galactic gas contents are likely the driving determinant for both the rise in SF and AGN activity from z = 5 to their peak at z = 2 and subsequent fall to lower z. We suggest that for self-gravitating clouds with supersonic turbulence, cloud collisions and the filamentary structure of the clouds regulate the star formation activity.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Abstract: We present the survey design, implementation, and outlook for COSMOS-Web, a
255 hour treasury program conducted by the James Webb Space Telescope in its
first cycle of observations. COSMOS-Web is a contiguous 0.54 deg$^2$ NIRCam
imaging survey in four filters (F115W, F150W, F277W, and F444W) that will reach
5$\sigma$ point source depths ranging $\sim$27.5-28.2 magnitudes. In parallel,
we will obtain 0.19 deg$^2$ of MIRI imaging in one filter (F770W) reaching
5$\sigma$ point source depths of $\sim$25.3-26.0 magnitudes. COSMOS-Web will
build on the rich heritage of multiwavelength observations and data products
available in the COSMOS field. The design of COSMOS-Web is motivated by three
primary science goals: (1) to discover thousands of galaxies in the Epoch of
Reionization ($6
Peer Review Status:Awaiting Review