Download Building` a Galaxy SED

AST4320 - Cosmology and extragalactic astronomy
AST4320 - Cosmology and extragalactic astronomy
Practical considerations
Mark Dijkstra, room 205
[email protected]
Max Gronke, room 216
[email protected]
AST4320 - Cosmology and extragalactic astronomy
Practical considerations
Class: Tuesday 14:15-16:00; Thursday 12:15-14:00 (Mark Dijkstra)
Exercises: Wednesday 12:15-14:00 (Max Gronke)
Important dates
Mid-term exam: October 7th. NO class on September 30 + October 2
Final exam on Dec 10:
No class on Nov 9 (MD gone)
Class replaced with Kavli seminar on September 11th. More info to follow....
AST4320 - Cosmology and extragalactic astronomy
Topics covered (broadly):
galaxy phenomenology
growth of structure in our Universe in linear + non-linear regimes (spherical collapse)
Gaussian random fields, Press-Schechter theory, dark matter halo mass functions
baryonic physics of galaxy formation (gas accretion, cooling, feedback processes)
formation & evolution of supermassive black holes
formation of first stars and galaxies, and the `dark ages’ & reionization of the Universe
open questions in galaxy formation/extragalactic astrophysics
Useful books: Galaxy Formation & Evolution, by Mo, van den Bosch & White.
Galaxy Formation, by Longair.
AST4320 - Cosmology and extragalactic astronomy
Topics covered (broadly):
Galaxy formation is deeply rooted in cosmology + requires broad understanding of astrophysics.
Overall goals are to
• develop a broad understanding of structure + galaxy formation.
• be able to read & broadly understand research literature in this field.
Useful books: Galaxy Formation & Evolution, by Mo, van den Bosch & White.
Galaxy Formation, by Longair.
AST4320 - Cosmology and extragalactic astronomy
Lecture 1: Galaxy Phenomenology*
Galaxy morphological classification.
Stellar types + their spectral energy distribution (SED).
Galaxy types and their SEDs.
Galaxy `colors’, a compact representation of their SED.
Color-selection of Lyman Break/drop-out galaxies.
* Galaxy phenomenology is an extensive subject. See Chapter 2 of Mo, Van
den Bosch & White, and Chapter 3 of Longair for more complete reviews.
Why care about galaxies?
Fundamental problem: We live in one, and want to understand our origin.
Why care about galaxies?
Fundamental problem: We live in one, and want to understand our origin.
Fun problem: galaxy astrophysics spans a wide range of scales: deeply rooted in
cosmology, large variation in physics (fluid dynamics, quantum physics)
Why care about galaxies?
Fundamental problem: We live in one, and want to understand our origin.
Fun problem: galaxy astrophysics spans a wide range of scales: deeply rooted in
cosmology, large variation in physics (fluid dynamics, quantum physics)
Practical problem: galaxies are biased tracers of underlying mass distribution. In order
to use galaxies to measure underlying mass distribution, we must understand galaxies.
Galaxy Phenomenology
Galaxy Phenomenology
Galaxy Phenomenology
Galaxy Phenomenology: Types/Classification
`early’ type
`late’ type
Hubble classification: a lot of physical quantities of galaxies correlate
with their classification (age, gas content,...)
Galaxy Phenomenology
`Most of our information on astronomical objects are derived from the radiation we receive
from it, or by the absorption it causes in the light of background sources.’ Mo, VdB, White
This information is encoded within the objects Spectral Energy Distribution (SED)
Measure flux (energy/time/area) in the wavelength range
Galaxy Phenomenology
`Most of our information on astronomical objects are derived from the radiation we receive
from it, or by the absorption it causes in the light of background sources.’ Mo, VdB, White
This information is encoded within the objects Spectral Energy Distribution (SED)
Measure flux (energy/time/area) in the frequency range
Often expressed as (AB)-magnitude:
(CGS units)
`Building’ a Galaxy SED
To first order, galaxy SED is a superposition of stellar SEDs
Stellar spectra have a ~ black-body shape.
`Building’ a Galaxy SED
Stellar spectra have a ~ black-body shape: characterized fully by T.
`Building’ a Galaxy SED
Stars populate a well-defined region in L-T space.
`Building’ a Galaxy SED
Stars populate a well-defined region in L-T space.
m=10msun
sun
`Building’ a Galaxy SED
Stars populate a well-defined region in L-T space.
`Building’ a Galaxy SED
Stars populate a well-defined region in L-T space.
Massive stars: young, very luminous, and high T (i.e. luminous in blue/UV)
Spectral Energy Distributions (SEDs) of different Stellar Types
UV
optical
IR
M-stars: cool, long-lived, low mass stars.
.
.
.
O-stars: hot, short-lived, massive stars
Spectral Energy Distributions (SEDs) of different Stellar Types
UV
optical
IR
M-stars: cool, long-lived, low mass stars.
.
SED peaks in optical/IR
.
.
O-stars: hot, short-lived, massive stars
SED peaks in UV
Spectral Energy Distributions (SEDs) of different Stellar Types
UV
optical
IR
M-stars: cool, long-lived, low mass stars.
.
SED peaks in optical/IR
.
.
O-stars: hot, short-lived, massive stars
SED peaks in UV
UV-emitting galaxies must contain young stars, and must have formed stars recently.
`Building’ a Galaxy SED
To first order, galaxy SED is a superposition of stellar SEDs
`Building’ a Galaxy SED
To first order, galaxy SED is a superposition of stellar SEDs
`Building’ a Galaxy SED
To first order, galaxy SED is a superposition of stellar SEDs
Star light is processes through interstellar gas, which contains HI.
`Building’ a Galaxy SED
To first order, galaxy SED is a superposition of stellar SEDs
Star light is processes through interstellar gas, which contains HI.
Photons with
can ionize H.
nks to:
`Building’ a Galaxy SED
Photons with
can ionize H.
Partridge & Peebles ‘67
nks to:
`Building’ a Galaxy SED
Photons with
can ionize H.
Partridge & Peebles ‘67
e
p
1s
nks to:
`Building’ a Galaxy SED
Photons with
can ionize H.
e
Partridge & Peebles ‘67
p
1s
nks to:
`Building’ a Galaxy SED
Recombination of proton & electron is followed by radiative cascade to ground state.
Partridge & Peebles ‘67
Gives rise to Lyman, Balmer, Paschen,...-series photons.
nks to:
`Building’ a Galaxy SED
Recombination of proton & electron is followed by radiative cascade to ground state.
Partridge & Peebles ‘67
HaHb
Recombination photons produced in HII nebulae around O & B stars: nebular lines.
nks to:
`Building’ a Galaxy SED
Recombination photons produced in HII nebulae around O & B stars: nebular lines.
Partridge & Peebles ‘67
[OII]
HaHb
Other emission lines from nebulae from heavier elements: e.g [OII3727], [OIII4959+5007]
nks to:
`Building’ a Galaxy SED
Interstellar gas outside HII regions contains HI, heavier elements, dust
Partridge & Peebles ‘67
[OII]
HaHb
CII, SiII, FeI
schematically
nks to:
`Building’ a Galaxy SED
Interstellar gas outside HII regions contains HI, heavier elements, dust
Partridge & Peebles ‘67
[OII]
HaHb
CII, SiII, FeI
schematically
nks to:
`Building’ a Galaxy SED
Interstellar gas outside HII regions contains HI, heavier elements, dust
Partridge & Peebles ‘67
[OII]
HaHb
CII, SiII, FeI
schematically
Dust consists of small particles consisting of a few molecules to micrometer size. Impact
extends beyond absorption lines, and is determined empirically via ‘extinction curve’.
nks to:
Extinction Curve
For solar metallicities, scales linearly with gas’ metallicity.
IR
optical
UV
Dust preferentially affects shorter wavelengths, and thus ‘reddens’ spectra.
Spectral Energy Distributions (SEDs) of different Galaxies
`E’ Galaxy contains mostly old stars
`starburst’ galaxy contains young stars
Galaxy SED contains information on its stellar populations + star formation history.
Spectral Energy Distributions (SEDs) of different Galaxies
Stacked spectrum of ~ 800 luminous star forming galaxies at z~3 in rest-frame UV.
Hard to get SED for all Galaxies
Parameterize SED in broad-band fluxes/colors
magnitude in some band:
Parameterize SED in broad-band fluxes/colors
magnitude in some* band:
* widely used Johnson-Cousins UVBRI-filter system covering optical. IR-filters
JHK cover bands where atmosphere is transparent. Space-based telescopes can
have entirely different sets. e.g Hubble X= F105W, ..., F160W, ...
Parameterize SED in broad-band fluxes/colors
magnitude in some band:
absolute magnitude (source at 10 pc):
Absolute Magnitude
Absolute magnitude is magnitude of source if it were located 10 pc away.
Apparent magnitude of sun is mV~-26. Absolute magnitude....
of sun is MV~4.8.
Absolute Magnitude
Absolute magnitude is magnitude of source if it were located 10 pc away.
Apparent magnitude of sun is mV~-26. Absolute magnitude....
of sun is MV~4.8.
of a massive O-star is MV~-5
Absolute Magnitude
Absolute magnitude is magnitude of source if it were located 10 pc away.
Apparent magnitude of sun is mV~-26. Absolute magnitude....
of sun is MV~4.8.
of a massive O-star is MV~-5
of a (Type 1a) supernova explosion MV~-19.3
Absolute Magnitude
Absolute magnitude is magnitude of source if it were located 10 pc away.
Apparent magnitude of sun is mV~-26. Absolute magnitude....
of sun is MV~4.8.
of a massive O-star is MV~-5
of a (Type 1a) supernova explosion MV~-19.3
of our Milky way as a whole MV~-20
brightest elliptical galaxies MV~-23
Absolute Magnitude
Absolute magnitude is magnitude of source if it were located 10 pc away.
Apparent magnitude of sun is mV~-26. Absolute magnitude....
of sun is MV~4.8.
of a massive O-star is MV~-5
of a (Type 1a) supernova explosion MV~-19.3
of our Milky way as a whole MV~-20
brightest elliptical galaxies MV~-23
brightest quasars MV~-30
Absolute Magnitude
Absolute magnitude is magnitude of source if it were located 10 pc away.
Apparent magnitude of sun is mV~-26. Absolute magnitude....
of sun is MV~4.8.
of a massive O-star is MV~-5
of a (Type 1a) supernova explosion MV~-19.3
of our Milky way as a whole MV~-20
brightest elliptical galaxies MV~-23
brightest quasars MV~-30
gamma-ray bursts MV~-36
Statistical Properties of Galaxies based on Abs. Magnitude/Color
Luminosity function: number density of galaxies as a function of abs. magnitude MX.
Luminosity function well described by Schechter function.
Intermezzo ‘h’
When distance derived from recessional velocity
Intermezzo ‘h’
When distance derived from recessional velocity
Statistical Properties of Galaxies based on Abs. Magnitude/Color
Luminosity function: number density of galaxies as a function of abs. magnitude MX.
normalization
Schechter function:
Statistical Properties of Galaxies based on Abs. Magnitude/Color
Luminosity function: number density of galaxies as a function of abs. magnitude MX.
`break’-luminosity
Schechter function:
Statistical Properties of Galaxies based on Abs. Magnitude/Color
Luminosity function: number density of galaxies as a function of abs. magnitude MX.
faint-end slope
Schechter function:
Statistical Properties of Galaxies based on Abs. Magnitude/Color
Luminosity function: number density of galaxies as a function of abs. magnitude MX.
Schechter function:
number density
diverges for
luminosity density
diverges for
For
faint galaxies dominate number density, bright galaxies luminosity density
Parameterize SED in broad-band fluxes/colors
magnitude in some band:
absolute magnitude (source at 10 pc):
Color:
Parameterize SED in broad-band fluxes/colors
Color:
Bluest filter first: higher number = redder.
Statistical Properties of Galaxies based on Abs. Magnitude/Color
Color distribution.
blue
red
bimodal color distribution
Statistical Properties of Galaxies based on Abs. Magnitude/Color
Color distribution.
blue
Color vs abs magnitude
red
red sequence
blue cloud
bimodal color distribution
Statistical Properties of Galaxies based on Abs. Magnitude/Color
Color distribution.
blue
Color vs abs magnitude
red
red sequence
green valley
blue cloud
bimodal color distribution
Statistical Properties of Galaxies based on Abs. Magnitude/Color
Galaxy color vs Hubble type. SG07 fig 5.25.
Using Galaxy Colors to Identify them
How to identify starforming galaxies at
z>3, z>4, z>5,
without having spectra for them?
Using Galaxy Colors to Identify them
How to identify starforming galaxies at z>3, z>4, z>5, without having spectra for them?
Recall: starforming galaxies contain young, hot massive stars.
Using Galaxy Colors to Identify them
How to identify starforming galaxies at z>3, z>4, z>5, without having spectra for them?
Recall: starforming galaxies contain young, hot massive stars.
Using Galaxy Colors to Identify them
How to identify starforming galaxies at z>3, z>4, z>5, without having spectra for them?
Recall: starforming galaxies contain young, hot massive stars.
C
absorption by HI
creates `break’ in spectrum
Intergalactic medium enhances this break further
Intergalactic Absorption: The Lya Forest
Diffuse overdense gas in intergalactic medium imposes additional absorption.
Using Galaxy Colors to Identify them
How to identify starforming galaxies at z>3, z>4, z>5, without having spectra for them?
Recall: starforming galaxies contain young, hot massive stars.
C
absorption by HI
creates `break’ in spectrum
This galaxy at z=3 visible
in G, R filter but vanishes
(`drops out’) from U filter.
Using Galaxy Colors to Identify them
How to identify starforming galaxies at z>3, z>4, z>5, without having spectra for them?
Recall: starforming galaxies contain young, hot massive stars.
C
absorption by HI
creates `break’ in spectrum
This galaxy at z=3 visible
in G, R filter but vanishes
(`drops out’) from U filter.
U drop-out or
Lyman Break galaxy (LBG)
Using Galaxy Colors to Identify them
A galaxy at z~3 `drops out’ of the U-band. z~3 galaxies are `U drop-outs’.
Similarly, z~4,5,6,... galaxies are B,V,and i drop-outs.
A z-dropout, later spectroscopically confirmed at z=7.51 (Finkelstein+2013, Nature)
Using Galaxy Colors to Identify them
A galaxy at z~3 `drops out’ of the U-band. z~3 galaxies are `U drop-outs’.
Similarly, z~4,5,6,... galaxies are B,V,and i drop-outs.
A z-dropout, later spectroscopically confirmed at z=7.51 (Finkelstein+2013, Nature)
Color/Broad-band/drop-out Selected Galaxies
Color/Broad-band/drop-out Selected Galaxies
Color/Broad-band/drop-out Selected Galaxies
Faint-end slope becomes steeper towards higher z, approaching -2.
Open question: how much radiation comes from faint, undetected galaxies?