The Cherenkov Telescope Array (CTA) is a new observatory for very high-energy (VHE) gamma rays. CTA has ambitions science goals, for which it is necessary to achieve full-sky coverage, to improve the sensitivity by about an order of magnitude, to span about four decades of energy, from a few tens of GeV to above 100 TeV with enhanced angular and energy resolutions over existing VHE gamma-ray observatories. An international collaboration has formed with more than 1000 members from 27 countries in Europe, Asia, Africa and North and South America. In 2010 the CTA Consortium completed a Design Study and started a three-year Preparatory Phase which leads to production readiness of CTA in 2014. In this paper we introduce the science goals and the concept of CTA, and provide an overview of the project. ?? 2013 Elsevier B.V. All rights reserved

3C 397 is a radio and X-ray bright Galactic supernova remnant (SNR) with an unusual rectangular morphology. Our CO observation obtained with the Purple Mountain Observatory at Delingha reveals that the remnant is well confined in a cavity of molecular gas, and embedded at the edge of a molecular cloud (MC) at the local standard of rest systemic velocity of ∼ 32 km s −1 . The cloud has a column density gradient increasing from southeast to northwest, perpendicular to the Galactic plane, in agreement with the elongation direction of the remnant. This systemic velocity places the cloud and SNR 3C 397 at a kinematic distance of ∼ 10.3 kpc. The derived mean molecular density (∼ 10-30 cm −3 ) explains the high volume emission measure of the X-ray emitting gas. A 12 CO line broadening of the ∼ 32 km s −1 component is detected at the westmost boundary of the remnant, which provides direct evidence of the SNR-MC interaction and suggests multi-component gas there with dense (∼ 10 4 cm −3 ) molecular clumps. We confirm the previous detection of a MC at ∼ 38 km s −1 to the west and south of the SNR and argue, based on HI self-absorption, that the cloud is located in the foreground of the remnant.A list of 64 Galactic SNRs presently known and suggested to be in physical contact with environmental MCs is appended in this paper.

Combining HI data from the Canadian Galactic Plane Survey (CGPS) and CO data from the Milky Way Imaging Scroll Painting (MWISP) project, we have identified a new segment of a spiral arm between Galactocentric radii of 15 and 19 kpc that apparently lies beyond the Outer Arm in the second Galactic quadrant. Over most of its length, the arm is 400-600 pc thick in z. The new arm appears to be the extension of the distant arm recently discovered by Dame & Thaddeus (2011) as well as the Scutum−Centaurus Arm into the outer second quadrant. Our current survey identified a total of 72 molecular clouds with masses on the order of 10 2 -10 4 M ⊙ that probably lie in the new arm. When all of the available data from the CO molecular clouds are fit, the best−fitting spiral model gives a pitch angle of 9.3 • ±0.7 • .

The Milky Way Imaging Scroll Painting (MWISP) project is an unbiased Galactic plane CO survey for mapping regions of l = −10 • to +250 • and |b| < ∼ 5. • 2 with the 13.7 m telescope of the Purple Mountain Observatory. The legacy survey aims to observe the 12 CO, 13 CO, and C 18 O (J=1-0) lines simultaneously with full-sampling using the nine-beam Superconducting SpectroScopic Array Receiver (SSAR) system with an instantaneous bandwidth of 1 GHz. In this paper, the completed 250 deg 2 data from l = +25. • 8 to +49. • 7 are presented with a grid spacing of 30 ′′ and a typical rms noise level of ∼ 0.5 K for 12 CO at the channel width of 0.16 km s −1 and ∼ 0.3 K for 13 CO and C 18 O at 0.17 km s −1 . The high-quality data with moderate resolution (∼50 ′′ ), uniform sensitivity, and high spatial dynamic range, allow us to investigate the details of molecular clouds (MCs) traced by the three CO isotope lines. Three interesting examples are briefly investigated, including distant Galactic spiral arms traced by CO emission with V LSR <0 km s −1 , the bubble-like dense gas structure near the H ii region W40, and the MCs distribution perpendicular to the Galactic plane.