Debris disks are believed to be related to planetesimals left over around stars after planet formation has ceased. The frequency of debris disks around M-dwarfs which account for 70% of the stars in the Galaxy is unknown while constrains have already been found for A-to K-type stars. We have searched for cold debris disks around 32 field M-dwarfs by conducting observations at λ = 850 µm with the SCUBA bolometer array camera at the JCMT and at λ = 1.2 mm with the MAMBO array at the IRAM 30-m telescopes. This is the first survey of a large sample of M-dwarfs conducted to provide statistical constraints on debris disks around this type of stars. We have detected a new debris disk around the M0.5 dwarf GJ 842.2 at λ = 850 µm, providing evidence for cold dust at large distance from this star (∼300 AU). By combining the results of our survey with the ones of Liu et al. (2004), we estimate for the first time the detection rate of cold debris disks around field M-dwarfs with ages between 20 and 200 Myr. This detection rate is 13 +6 −8 % and is consistent with the detection rate of cold debris disks (9-23%) around A-to K-type main sequence stars of the same age. This is an indication that cold disks may be equally prevalent across stellar spectral types.

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Context. Millimetre-wave continuum astronomy is today an indispensable tool for both general astrophysics studies (e.g. star formation, nearby galaxies) and cosmology (e.g. cosmic microwave background and high-redshift galaxies). General purpose, large-fieldof-view instruments are needed to map the sky at intermediate angular scales not accessible by the high-resolution interferometers (e.g. ALMA in Chile, NOEMA in the French Alps) and by the coarse angular resolution space-borne or ground-based surveys (e.g. Planck, ACT, SPT). These instruments have to be installed at the focal plane of the largest single-dish telescopes, which are placed at high altitude on selected dry observing sites. In this context, we have constructed and deployed a three-thousand-pixel dual-band (150 GHz and 260 GHz, respectively 2 mm and 1.15 mm wavelengths) camera to image an instantaneous circular field-of-view of 6.5 arcmin in diameter, and configurable to map the linear polarisation at 260 GHz. Aims. First, we are providing a detailed description of this instrument, named NIKA2 (New IRAM KID Arrays 2), in particular focussing on the cryogenics, optics, focal plane arrays based on Kinetic Inductance Detectors, and the readout electronics. The focal planes and part of the optics are cooled down to the nominal 150 mK operating temperature by means of an adhoc dilution refrigerator. Secondly, we are presenting the performance measured on the sky during the commissioning runs that took place between October 2015 and April 2017 at the 30-m IRAM telescope at Pico Veleta, near Granada (Spain). Methods. We have targeted a number of astronomical sources. Starting from beam-maps on primary and secondary calibrators we have then gone to extended sources and faint objects. Both internal (electronic) and on-the-sky calibrations are applied. The general methods are described in the present paper. Results. NIKA2 has been successfully deployed and commissioned, performing in-line with expectations. In particular, NIKA2 exhibits full width at half maximum angular resolutions of around 11 and 17.5 arcsec at respectively 260 and 150 GHz. The noise equivalent flux densities are, at these two respective frequencies, 33 ± 2 and 8 ± 1 mJy s 1/2 . A first successful science verification run was achieved in April 2017. The instrument is currently offered to the astronomy community and will remain available for at least the following ten years.Key words. instrumentation: detectors -instrumentation: photometers -instrumentation: polarimeters -submillimeter: ISMsubmillimeter: galaxies -cosmic background radiation Article published by EDP Sciences A115, page 1 of 15 A&A 609, A115 (2018)

Debris disks have been found primarily around intermediate and solar mass stars (spectral types A-K) but rarely around low mass M-type stars. We have spatially resolved a debris disk around the remarkable M3-type star GJ 581 hosting multiple planets using deep PACS images at 70, 100 and 160 μm as part of the DEBRIS Program on the Herschel Space Observatory. This is the second spatially resolved debris disk found around an M-type star, after the one surrounding the young star AU Mic (12 Myr). However, GJ 581 is much older (2-8 Gyr), and is X-ray quiet in the ROSAT data. We fit an axisymmetric model of the disk to the three PACS images and found that the best fit model is for a disk extending radially from 25 ± 12 AU to more than 60 AU. Such a cold disk is reminiscent of the Kuiper belt but it surrounds a low mass star (0.3 M ) and its fractional dust luminosity L dust /L * of ∼10 −4 is much higher. The inclination limits of the disk found in our analysis make the masses of the planets small enough to ensure the long-term stability of the system according to some dynamical simulations. The disk is collisionally dominated down to submicron-sized grains and the dust cannot be expelled from the system by radiation or wind pressures because of the low luminosity and low X-ray luminosity of GJ 581. We suggest that the correlation between low-mass planets and debris disks recently found for G-type stars also applies to M-type stars. Finally, the known planets, of low masses and orbiting within 0.3 AU from the star, cannot dynamically perturb the disk over the age of the star, suggesting that an additional planet exists at larger distance that is stirring the disk to replenish the dust.

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We present observations of ǫ Eridani from the Submillimeter Array (SMA) at 1.3 millimeters and from the Australia Telescope Compact Array (ATCA) at 7 millimeters that reach an angular resolution of ∼ 4 ′′ (13 AU). These first millimeter interferometer observations of ǫ Eridani, which hosts the closest debris disk to the Sun, reveal two distinct emission components: (1) the well-known outer dust belt, which, although patchy, is clearly resolved in the radial direction, and (2) an unresolved source coincident with the position of the star. We use direct model-fitting of the millimeter visibilities to constrain the basic properties of these two components. A simple Gaussian shape for the outer belt fit to the SMA data results in a radial location of 64.4 +2.4 −3.0 AU and FWHM of 20.2 +6.0 −8.2 AU

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Serendipitously we have discovered a rare, bright submillimeter galaxy (SMG) with a flux density of 30 ± 2 mJy at λ = 1.2 mm, using MAMBO2 at the IRAM 30-m millimeter telescope. Although no optical counterpart is known for MM18423+5938, we were able to measure the redshift z = 3.92960 ± 0.00013 from the detection of CO lines using the IRAM Eight MIxer Receiver (EMIR). In addition, by collecting all available photometric data in the far-infrared and radio to constrain its spectral energy distribution, we derive the FIR luminosity 4.8 × 10 14 /m L and mass 6.0 × 10 9 /m M for its dust, allowing for a magnification factor m caused by a probable gravitational lens. The corresponding star-formation rate is 8.3 × 10 4 /m M /yr. The detection of three lines of the CO rotational ladder, and a significant upper limit for a fourth CO line, allow us to estimate an H 2 mass of between 1.9 × 10 11 /m M and 1.1 × 10 12 /m M . The two lines C I( 3 P 1 − 3 P 0 ) and C I( 3 P 2 − 3 P 1 ) were clearly detected and yield a [