Psicologia e práticas sociais

Rieke

et al. 2019

ApJ

We present high-fidelity, 30 milliarcsecond (200-pc) resolution ALMA rest-frame 240 µm observations of cold dust emission in three typical main-sequence star-forming galaxies (SFGs) at z ∼ 3 in the Hubble Ultra-Deep Field (HUDF). The cold dust is distributed within the smooth disk-like central regions of star formation 1 − 3 kpc in diameter, despite their complex and disturbed rest-frame UV and optical morphologies. No dust substructures or clumps are seen down to 1 − 3 M yr −1 (1σ) per 200-pc beam. No dust emission is observed at the locations of UV-emitting clumps, which lie 2 − 10 kpc from the bulk of star formation. Clumpy substructures can contribute no more than 1 − 7% of the total star formation in these galaxies (3σ upper limits). The lack of star-forming substructures in our HUDF galaxies is to be contrasted with the multiple substructures characteristic of submillimeter-selected galaxies (SMGs) at the same cosmic epoch, particularly the far-IR-bright SMGs with similarly high-fidelity ALMA observations of Hodge et al. (2019). Individual star-forming substructures in these SMGs contain ∼ 10 − 30% of their total star formation. A substructure in these SMGs is often comparably bright in the far-infrared as (or in some cases brighter than) our typical SFGs, suggesting that these SMGs originate from a class of disruptive event involving multiple objects at the scale of our HUDF galaxies. The scale of the disruptive event found in our main-sequence SFGs, characterized by the lack of star-forming substructures at our resolution and sensitivity, could be less violent, e.g., gas-rich disk instability or minor mergers.

Section: Smoothness Of the Cold Dust Distributionsmentioning

confidence: 99%

ALMA 200 pc Resolution Imaging of Smooth Cold Dusty Disks in Typical z ∼ 3 Star-forming Galaxies

Rujopakarn

Rieke

et al. 2019

ApJ

“…One interesting path would be comparing to [CI] derived excitation temperatures, given that [CI] lines should remain thin (I. Cortzen et al 2019, in preparation). Another possibility would be to use [CII]λ158µm as a direct tracer of the gas mass (Zanella et al 2018) and from there more realistic M dust estimates via assumptions of G/D ratios (keeping in mind that [CII] could be heavily affected by optical depth effects). More observations are also needed to establish whether these cold (or apparently cold) SEDs are prevalent in the distant Universe, and if the optically thick case could provide a general explanation for the odd inversion that seems to take place at high redshifts, with SB galaxies becoming colder than MS galaxies.…”

Section: Optically Thick Dust Emission In the Fir?mentioning

confidence: 99%

Discovery of Four Apparently Cold Dusty Galaxies at z = 3.62–5.85 in the COSMOS Field: Direct Evidence of Cosmic Microwave Background Impact on High-redshift Galaxy Observables

Jin

Magdis

et al. 2019

ApJ

107

We report Atacama Large Millimetre Array (ALMA) observations of four high-redshift dusty star-forming galaxy candidates selected from far-Infrared (FIR)/submm observations in the COSMOS field. We securely detect all galaxies in the continuum and spectroscopically confirm them at z=3.62-5.85 using ALMA 3mm line scans, detecting multiple CO and/or [CI] transitions. This includes the most distant dusty galaxy currently known in the COSMOS field, ID85001929 at z=5.847. These redshifts are lower than we had expected as these galaxies have substantially colder dust temperatures than most literature sources at z>4. We provide direct evidence that, given their cold spectral energy distributions, CMB plays a significant role biasing their observed Rayleigh-Jeans (RJ) slopes to unlikely steep values and, possibly, reducing their CO fluxes by a factor of two. We recover standard RJ slopes when the CMB contribution is taken into account. High resolution ALMA imaging shows compact morphology and evidence for mergers. This work reveals a population of cold dusty star-forming galaxies that were under-represented in current surveys, and are even colder than typical Main Sequence galaxies at the same redshift. The observed cold dust temperatures could be a result of low star formation efficiency with rapid metal enrichment or, more likely, evidence for optically thick dust continuum in the FIR. High FIR dust optical depth might be a widespread feature of compact starbursts at any redshift.

“…Various works show that obscured SF is hosted in compact regions of massive Main Sequence (MS) galaxies (Tadaki et al 2017;Elbaz et al 2018), sub-millimeter galaxies (SMGs, Miettinen et al 2017;Hodge et al 2016;Fujimoto et al arXiv:1905.02958v1 [astro-ph.GA] 8 May 2019 2018) and "blue nuggets" (Barro et al 2016). On the other hand, stacking ALMA images in the uv plane reveals that "typical" high-z galaxies host extended obscured SF (Lindroos et al 2016;Zanella et al 2018).…”

Section: Introductionmentioning

confidence: 99%

The Main Sequence at z ∼ 1.3 Contains a Sizable Fraction of Galaxies with Compact Star Formation Sizes: A New Population of Early Post-starbursts?

Puglisi

Liu

et al. 2019

ApJL

110

ALMA measurements for 93 Herschel -selected galaxies at 1.1 z 1.7 in COSMOS reveal a sizable (> 29%) population with compact star formation (SF) sizes, lying on average > ×3.6 below the optical stellar mass (M )-size relation of disks. This sample widely spans the star-forming Main Sequence (MS), having 10 8 M 10 11.5 M and 20 SF R 680 M yr −1 . The 32 size measurements and 61 upper limits are measured on ALMA images that combine observations of CO(5-4), CO(4-3), CO(2-1) and λ obs ∼ 1.1−1.3 mm continuum, all tracing the star-forming molecular gas. These compact galaxies have instead normally extended K band sizes, suggesting strong specific SF R gradients. Compact galaxies comprise the 50 ± 18% of MS galaxies at M > 10 11 M . This is not expected in standard bi-modal scenarios where MS galaxies are mostly steadily-growing extended disks. We suggest that compact MS objects are early post-starburst galaxies in which the merger-driven boost of SF has subsided. They retain their compact SF size until either further gas accretion restores pre-merger galaxy-wide SF, or until becoming quenched. The fraction of merger-affected SF inside the MS seems thus larger than anticipated and might reach ∼ 50% at the highest M . The presence of large galaxies above the MS demonstrates an overall poor correlation between galaxy SF size and specific SF R.