Download Great Observatories Origins Deep Survey (GOODS) Observation

WELCOME TO
ASTRO330
Special Topics in Astrophysics
Fall 2016
Image of the deep space, up to ~1/2 billion year after the Big Bang, taken
with the Hubble Space Telescope
Contact Information
• Dr. Mauro Giavalisco:
– Room LGRT-B 520; phone: 413-545-4767
– Office Hours: T/T 2:00 – 3:00, or by appointment
– Email: [email protected]
Philosophy of the Course
• This course consists of some carefully selected topics in astrophysics.
It focuses on practical issues, as well as on current research and open
questions, mostly in extragalactic research. These will include:
– Observations; telescopes, instrumentation, data reduction
– Modern astronomical practice: photometry, morphology, properties of sources
– Review of current research and open questions: cosmology, star formation and
galaxy evolution, cosmic structures, the dark sector (matter and energy)
• The goal is to discuss modern astronomical facilities and practice, as
well as the state of current research so that if you choose astronomy as
a profession, you know what is going on in today’s research (at least
in extragalactic astronomy). It probably is the first time you are
exposed to what is currently going on in astronomy.
• While the course covers both theoretical and observational issues, it
focuses on how to measure the relevant physical properties, and it
provides guidelines on how to carry out astronomical observations,
use the data and interpret them.
Format of the Course
• Course material will be covered in two weekly lessons (Mo/We), 1hr15m long;
studying from my notes and selected papers, texts.
• It includes homework.
• The syllabus of the course will soon be online, together with most of the material
covered in class. The Web site is: www.astro.umass.edu/~mauro/astro330
• Ample opportunity for interactions: ASK QUESTIONS, when you need to.
REMEMBER:
– there are no stupid questions, except one: the one you never dared to ask!
– (there are stupid answers, however).
• This is critical: do not hesitate to seek help if you feel you are lagging behind!
– Past a given point, you will not be able to catch up and you will be lost and fail the course.
• My ultimate goal is to make you a competitive, independent scientist, capable to
conduct quantitative creative, hopefully innovative, research.
Course Requirements
• Grades: will be assigned on a modified straight scale. Scores will be
adjusted upward if the assignments/exams are too hard
• Guaranteed minimum grade:
–
–
–
–
–
A:
A-:
B:
B-:
C:
92%
87%
82%
77%
<72%
• Totals of components of Final Grade
– Final project:………………….………... 40%
– Homework:…………………..………… 20%
– Term Papers or Research Projects:…….. 40%
We have made tremendous progress in
understanding the evolution of the
universe: the Big Bang theory
t=0: the cosmic
expansion begins from
a singularity.
The density of energy
and mass and the
temperature are
infinite. The universe
keeps expanding at a
very fast rate and cools
down
t≈500,000 years: the
earliest visible universe:
the cosmic background
The dark age
t≈200,000,000: the first
stars, black holes and
galaxies form, the first
sources of light appear
t=13.8 billion years:
today. The cosmic
temperature is 2.7 K
But together with some answers, we also got new, more
profound questions: e.g. dark matter and dark energy
Most of the
mass of
galaxies is in
the form of
dark matter
Luminous
matter
amounts to
only ≈10%
What is it?
Theiry DOES
NOT predict it!
Time in billions of years
0.5
2.2
5.9
8.6
13.8
35
70
93
140
Quantum
fluctuations
13
D.M. is key to explain the universe: simulations show
that the gravity of dark matter pulls mass into denser
regions – universe grows lumpier with time, and the
simulated structures are very similar to the observed
ones
dr/r grows ~a(t): from z ~1,100 to today increased 1,000 times
Structures in galaxy maps are quantitatively very similar to the
ones found in simulations dark matter dominated universe
Dark energy: evidence in the
accelerated expansion of the universe
Brightness of distant white-dwarf supernovae tells us how much
universe has expanded since they exploded because their
luminosity at peak is ≈the same
Accelerating universe is best fit to supernova data
Dark Energy is what accelerates the expansion. But what is
it? Big mystery: no theory can predict it
Astronomy refresher: when we look at the universe,
what we see is sources on the Celestial Sphere
To make physical sense of the
universe we need to unambiguously
measure positions of sources in space.
Celestial objects at different distances
all appear projected on the celestial
sphere.
All we can really measure directly are
angular positions on the celestial
sphere.
The measure of distance (i.e. radial
distance to the source) is one of the
greatest problems of astronomy.
(the other is the measure of mass)
Angular Measurements
(just in case…)
• Full circle = 360º = 2p
• 1º = 60 (arcminutes)
• 1 = 60 (arcseconds)
•1 radian (p) = 57.2957795º =
3,437.74677 = 206,264.806
Review: Coordinates on the Earth (spherical)
• Latitude: position north or south of equator
• Longitude: position east or west of prime meridian
(runs through Greenwich, England)
Our view from Earth:
• Stars near the north celestial pole are circumpolar and
never set.
• We cannot see stars near the south celestial pole.
• All other stars (and Sun, Moon, planets) rise in east and
set in west.
A circumpolar star
never sets
Celestial Equator
Your Horizon
This star never
rises
The sky varies with latitude but
not longitude.
Length of a Day
• Solar day:
defined respect
to the Sun. The
Sun makes one
circuit around the
sky in 24 hours
Length of a Day
• Sidereal day:
defined respect to
distant stars.
Earth rotates once
on its axis in 23
hrs, 56 min, and
4.07 sec.
Length of a Day
• Solar day is longer than a sidereal day by about 1/360
because Earth moves about 1° in orbit each day
Mean Solar Time
• Length of an apparent solar
day changes during the year
because Earth’s orbit is
slightly elliptical.
• Mean solar time is based on
the average length of a day.
• Noon is average time at
which Sun crosses meridian
• It is a local definition of time
Universal Time (by the Sun)
• Universal time (UT or UTC) is defined to be
the mean solar time at 0° longitude.
• It is also known as Greenwich Mean Time
(GMT) because 0° longitude is defined to pass
through Greenwich, England
• It is the standard time used for astronomy and
navigation around the world
• Also, commonly referred to as the “Zulu Time”
Our Position around the Sun
• As the Earth orbits the Sun, the Sun appears to move eastward
along the ecliptic.
• At midnight, the stars on our meridian are opposite the Sun in
the sky.
How do we locate objects on the
celestial sphere?
Insert TCP 5e Figure
S1.8
• Coordinate the space by means of
static reference points in the sky.
• Four such (quasi) static points are
the equinoxes and solstices.
• We use the Spring Solstice as the
zero point of one coordinate.
• CAUTION! The solstice actually
precesses (50/yr), thus one MUST
specify the year.
• The 1950 Equinox and the 2000
Equinox (J2000) are the most
commonly used (the J2000 is the
most widely adopted one).
• Too many astronomers have
pointed the telescope to the wrong
place because they did not pay
attention to the year of the
equinox!!!
Solstices & Equinoxes
Celestial Coordinates
• Right ascension: Like longitude on celestial sphere
(measured in hours with respect to spring equinox).
• Declination: Like latitude on celestial sphere (measured
in degrees above celestial equator)
Time by the Stars
• Sidereal Time is the time measured from meridian
passage, in units of the sidereal day (i.e. dividing the S.D.
in 24 hr, then min, then sec). Sidereal time < Solar time
• The local sidereal time is 0h0m when the spring equinox
passes through the meridian
• Sidereal time is equal to right ascension that is passing
through the meridian
• A star’s hour angle is the time since it last passed through
the meridian
Local sidereal time = RA + hour angle
Example: Celestial Coordinates of Vega
• Right ascension:
Vega’s RA of 18h35.2m
(out of 24h) places most
of the way around
celestial sphere from
spring equinox.
• Declination: Vega’s
dec of +38°44’ puts it
almost 39° north of
celestial equator
(negative dec would be
south of equator)
Unit of length in astronomy: the parsec
When is p=1 arcsec,
D = 1 parsec (pc)
1 pc = 3.806x1018 cm
It takes light 3.26 years to
cover 1 pc
Imaging: what is an image?
Near-Infrared image, about 2,200 nm
An image is a spatial map
of the intensity of light
from a source, at some
wavelength recorded on a
detector (array of
photosensitive elements
or “pixels”)
The detector records the spatial distribution
of light intensity at the position of each
pixel
PIXEL: the smallest element of the image
that the camera can record
Imaging: filters
Images of astronomical sources are
always taken through some passband
(filter).
The filter lets only some wavelengths to
pass and reach the detector, and blocks
all the other.
The idea is to image the source only in
the selected range of wavelengths
The purposes of imaging are
1) measure the amount of light emitted
(photometry)
2) obtain the morphology
NOTE: due to motion or redshift, the
observed wavelength DOES NOT
correspond to the rest-frame wavelength
M. Giavalisco
Cosmological redshift:
Light needs time to travel across large volumes of space.
During this time the expansion of the universe continues
The apparent wavelength of light is increased as it
travels through an expanding space
The observed wavelength λo is longer than the emitted
wavelength λe
The redshift parameter z:
λo = λe x (1+z)
The effect of redshift
M. Giavalisco
34
Image Quality (resolution)
Diffraction limit: the image of point
source through an optical system has a
finite size, the Airy disk:
2αA
84% of energy
Sharp telescopes have thin PSF’s
HST with spherical aberration
(flowed mirror)
HST after the repair
Images with bad (left) and good (right) PSF
HST with flawed mirror
HST after the repair
On the ground, image quality is limited by
atmospheric seeing
Typical optical seeing:
FWHM = 0.5 – 1.5 arcsec
1.0 typical
0.3 exceptionally good
3.0 exceptionally bad
Image quality DOES the trick!!
To study faint galaxies both space-based sensitivity and angular resolution required!!
Note how many more details and faint objects can be observed with the HST
Subaru + SUPREME
HST + ACS